C# intelliSense intermittently failing/very slow when C# extension is running

[chris-combes]

Environment data

C# extension version 2.87.31

.NET SDK:
Version: 9.0.304
Commit: f12f5f689e
Workload version: 9.0.300-manifests.ad61bb1c
MSBuild version: 17.14.16+5d8159c5f

Runtime Environment:
OS Name: Windows
OS Version: 10.0.26100
OS Platform: Windows
RID: win-x64
Base Path: C:\Program Files\dotnet\sdk\9.0.304\

.NET workloads installed:
There are no installed workloads to display.
Configured to use loose manifests when installing new manifests.

Host:
Version: 9.0.8
Architecture: x64
Commit: aae90fa090

.NET SDKs installed:
6.0.428 [C:\Program Files\dotnet\sdk]
8.0.413 [C:\Program Files\dotnet\sdk]
9.0.304 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.19 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.19 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.19 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 9.0.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
x86 [C:\Program Files (x86)\dotnet]
registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
Not set

global.json file:
Not found

C# logs

2025-09-08 08:34:19.452 [trace] Activating C# Extension
2025-09-08 08:34:19.452 [trace] C# Extension activated in 115.079ms.

Steps to reproduce

1. Open VSCode
2. Wait for extensions to fully load
3. In a piece of C# code type 'Console.Wri'

Expected behavior

• Dropdown list with 'WriteLine' to appear

Actual behavior

• Dropdown list does not appear
• 'Loading' tooltip appears when I hover over 'Console.'

Additional context

• Occasionally IntelliSense does work with C# extension running (particularly if I have installed and reinstalled it). However eventually it stops working again in the VSCode session
• Worked OK until last few weeks. I have switched from a laptop running Windows 10 to one using Windows 11 in that time, so maybe that is linked
• If I disable the C# extension IntelliSense works fine
• I am running the C# extension together with OmniSharp

[JoeRobich]

I am running the C# extension together with OmniSharp

@chris-combes Can you share the output of the OmniSharp log from the VS Code Output pane?

[chris-combes]

Hi @JoeRobich - please find below the OmniSharp log output when I open VSCode :
Starting OmniSharp server at 9/11/2025, 8:20:40 AM
Target: c:\Users\CombesC\source\repos\SMFAutomatedTestsSSH2\SMFAutomatedTests\IRT.SMF.AutomatedTests.sln

OmniSharp server started with .NET 9.0.304
 (C:\Program Files\dotnet).
    Path: C:\Program Files\dotnet
    PID: -1

[Info  - 8:21:04 AM] OmniSharp.Services.DotNetCliService: Checking the 'DOTNET_ROOT' environment variable to find a .NET SDK | 
[Info  - 8:21:04 AM] OmniSharp.Services.DotNetCliService: Using the 'dotnet' on the PATH. | 
[Info  - 8:21:04 AM] OmniSharp.Services.DotNetCliService: DotNetPath set to dotnet | 
[Info  - 8:21:11 AM] OmniSharp.MSBuild.Discovery.MSBuildLocator: Located 2 MSBuild instance(s)
            1: .NET Core SDK 8.0.413 17.11.38 - "C:\Program Files\dotnet\sdk\8.0.413"
            2: .NET SDK 8.0.413 from C:\Program Files\dotnet\sdk\8.0.413 8.0.413 - "C:\Program Files\dotnet\sdk\8.0.413" | 
[Warn  - 8:21:11 AM] OmniSharp.CompositionHostBuilder: It looks like you have overridden the version of MSBuild with a version lower than 16.3 which is the minimum supported by the configured .NET Core Sdk.
 Try updating your MSBuild to version 16.3 or higher to enable better .NET Core Sdk support. | 
[Info  - 8:21:11 AM] OmniSharp.MSBuild.Discovery.MSBuildLocator: Registered MSBuild instance: .NET SDK 8.0.413 from C:\Program Files\dotnet\sdk\8.0.413 8.0.413 - "C:\Program Files\dotnet\sdk\8.0.413" | 
[Info  - 8:21:17 AM] OmniSharp.WorkspaceInitializer: Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpFormattingWorkspaceOptionsProvider, Order: 0 | 
[Info  - 8:21:18 AM] OmniSharp.Cake.CakeProjectSystem: Detecting Cake files in 'c:\Users\CombesC\source\repos\SMFAutomatedTestsSSH2\SMFAutomatedTests\'. | 
[Info  - 8:21:18 AM] OmniSharp.Cake.CakeProjectSystem: Did not find any Cake files | 
[Info  - 8:21:19 AM] OmniSharp.MSBuild.ProjectSystem: Skip loading projects listed in solution file or under target directory because MsBuild:LoadProjectsOnDemand is true. | 
[Info  - 8:21:19 AM] OmniSharp.Script.ScriptProjectSystem: Detecting CSX files in 'c:\Users\CombesC\source\repos\SMFAutomatedTestsSSH2\SMFAutomatedTests\'. | 
[Info  - 8:21:20 AM] OmniSharp.Script.ScriptProjectSystem: Did not find any CSX files | 
[Info  - 8:21:20 AM] OmniSharp.Roslyn.CSharp.Services.Diagnostics.CSharpDiagnosticWorkerWithAnalyzers: Solution initialized -> queue all documents for code analysis. Initial document count: 0. | 
[Info  - 8:21:20 AM] OmniSharp.WorkspaceInitializer: Configuration finished. | 
[Info  - 8:21:20 AM] OmniSharp.WorkspaceInitializer: Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpFormattingWorkspaceOptionsProvider, Order: 0 | 
[Info  - 8:21:20 AM] OmniSharp.WorkspaceInitializer: Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpFormattingWorkspaceOptionsProvider, Order: 0 | 
[Info  - 8:21:20 AM] OmniSharp.WorkspaceInitializer: Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpFormattingWorkspaceOptionsProvider, Order: 0 | 
[Info  - 8:21:20 AM] OmniSharp.WorkspaceInitializer: Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpFormattingWorkspaceOptionsProvider, Order: 0 | 
[Info  - 8:21:20 AM] OmniSharp.LanguageServerProtocol.LanguageServerHost: Omnisharp server running using Lsp at location 'c:\Users\CombesC\source\repos\SMFAutomatedTestsSSH2\SMFAutomatedTests\' on host 18936. | 

[JoeRobich]

@chris-combes This seems to be the issue.

[Warn  - 8:21:11 AM] OmniSharp.CompositionHostBuilder: It looks like you have overridden the version of MSBuild with a version lower than 16.3 which is the minimum supported by the configured .NET Core Sdk.
 Try updating your MSBuild to version 16.3 or higher to enable better .NET Core Sdk support

Are you using an omnisharp.json for configuration? Can you share it if so?

Are you configuring omnisharp.* settings in VS Code? Can you share them if so?

[chris-combes]

Hi @JoeRobich - sorry for the delay in replying.

The MSBuild message is a bit odd as I have got a whole host of MSBuild.exe and MSBuild.dll s on my machine including some that are at v17.x. This includes the one in c:\program files\dotnet\sdk\8.0.413 which omnisharp seems to be looking at

[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Located 2 MSBuild instance(s)
            1: .NET Core SDK 8.0.413 17.11.38 - "C:\Program Files\dotnet\sdk\8.0.413"
            2: .NET SDK 8.0.413 from C:\Program Files\dotnet\sdk\8.0.413 8.0.413 - "C:\Program Files\dotnet\sdk\8.0.413"
[warn]: OmniSharp.CompositionHostBuilder
        It looks like you have overridden the version of MSBuild with a version lower than 16.3 which is the minimum supported by the configured .NET Core Sdk.
 Try updating your MSBuild to version 16.3 or higher to enable better .NET Core Sdk support.

I wonder if my path environment variables are forcing omnisharp to look at an older version.

In terms of the settings files

• I'm not using a omnisharp.json file
• Here is my user vscode settings file

{
    "sqldeveloper.sqlHistory.historyLimit": 500,
    "chat.instructionsFilesLocations": {
        ".github/instructions": true,
        "C:\\Users\\CombesC\\AppData\\Local\\Temp\\postman-collections-post-response.instructions.md": true,
        "C:\\Users\\CombesC\\AppData\\Local\\Temp\\postman-collections-pre-request.instructions.md": true,
        "C:\\Users\\CombesC\\AppData\\Local\\Temp\\postman-folder-post-response.instructions.md": true,
        "C:\\Users\\CombesC\\AppData\\Local\\Temp\\postman-folder-pre-request.instructions.md": true,
        "C:\\Users\\CombesC\\AppData\\Local\\Temp\\postman-http-request-post-response.instructions.md": true,
        "C:\\Users\\CombesC\\AppData\\Local\\Temp\\postman-http-request-pre-request.instructions.md": true
    },
    "sqldeveloper.telemetry.enabled": false,
    "files.autoSave": "afterDelay",
    "omnisharp.disableMSBuildDiagnosticWarning": true,
	"omnisharp.path": "C:\\Program Files\\omnisharp\\omnisharp.exe",
    "csharp.suppressProjectJsonWarning": true,
    "cSpell.language": "en-GB",
    "telemetry.feedback.enabled": false,
    "telemetry.editStats.enabled": false,
    "telemetry.telemetryLevel": "off",
    "dotnetAcquisitionExtension.enableTelemetry": false,
    "gitlens.telemetry.enabled": false,
    "postman.telemetry.enabled": false,
    "NugetGallery.credentialProviderFolder": "{user-profile}/.nuget/plugins/netcore/CredentialProvider.Microsoft",
    "NugetGallery.skipRestore": "false",
    "NugetGallery.sources": [
        "{\"name\":\"nuget.org\",\"url\":\"https://api.nuget.org/v3/index.json\"}"
    ],
    "git.autofetch": true,
    "mssql.connectionGroups": [
        {
            "name": "ROOT",
            "id": "8B1F3826-44EF-49E3-BC69-E71AEB308909"
        }
    ],
    "github.copilot.chat.agent.autoFix": false,
    "github.copilot.chat.agent.runTasks": false,
    "github.copilot.chat.codeGeneration.useInstructionFiles": false,
    "github.copilot.chat.customInstructionsInSystemMessage": false,
    "github.copilot.chat.useProjectTemplates": false,
    "github.copilot.editor.enableCodeActions": false,
    "github.copilot.nextEditSuggestions.fixes": false,
    "github.copilot.renameSuggestions.triggerAutomatically": false,
    "github.copilot.chat.copilotDebugCommand.enabled": false,
    "github.copilot.chat.reviewSelection.enabled": false,
    "github.copilot.chat.startDebugging.enabled": false,
    "github.copilot.chat.agent.currentEditorContext.enabled": false,
    "github.copilot.chat.edits.newNotebook.enabled": false,
    "github.copilot.chat.edits.suggestRelatedFilesForTests": false,
    "github.copilot.chat.edits.suggestRelatedFilesFromGitHistory": false,
    "github.copilot.chat.newWorkspaceCreation.enabled": false,
    "github.copilot.chat.setupTests.enabled": false,
    "github.copilot.chat.summarizeAgentConversationHistory.enabled": false,
    "chat.agent.enabled": false,
    "chat.commandCenter.enabled": false,
    "chat.notifyWindowOnConfirmation": false,
    "sonarlint.focusOnNewCode": false,
    "editor.minimap.enabled": false,
    "git.enableSmartCommit": true,
    "csharpsortusings.sort.usings.order": "System",
    "sonarlint.pathToNodeExecutable": "C:\\Program Files\\nodejs\\node.exe",
    "github.copilot.enable": {
        "*": false,
    },
    "github.copilot.inlineSuggest.enable": false,
    "omnisharp.enableDecompilationSupport": true,
    "editor.stickyScroll.enabled": false,
    "omnisharp.sdkPath": "C:\\Program Files\\dotnet\\sdk\\8.0.413",
    "omnisharp.sdkVersion": "8.0.413",
    "omnisharp.dotnetPath": "C:\\Program Files\\dotnet",
    "omnisharp.enableMsBuildLoadProjectsOnDemand": true,
    "dotnet.completion.showCompletionItemsFromUnimportedNamespaces": false,
    "omnisharp.projectLoadTimeout": 120,
    "postman.mcp.notifications.postmanMCP": false,
    "intellicodeCompletions.runAlongsideCopilot": true,
    "editor.defaultFormatter": "ms-dotnettools.csharp",
    "editor.defaultFoldingRangeProvider": "ms-dotnettools.csharp",
    "razor.languageServer.cohostingEnabled": false,
    "razor.languageServer.useNewFormattingEngine": false,
    "razor.languageServer.suppressLspErrorToasts": false,
    "razor.format.enable": false,
    "typescript.tsserver.web.projectWideIntellisense.enabled": false,
    "dotnet.completion.provideRegexCompletions": false,
    "dotnet.enableXamlTools": false,
    "csharp-ls.csharp-ls-executable": "csharp-ls",
    "[csharp]": {
        "editor.defaultFormatter": "ms-dotnettools.csharp"
    },
    "dotnet.server.useOmnisharp": true,
    "csharp.showOmnisharpLogOnError": false,
    "sonarlint.automaticAnalysis": false,
    "editor.codeActionsOnSave": {
        
    }
}

• Here is the vscode workspace settings.json file for the solution I am using

{
    "csharp.format.enable": false,
    "csharp.semanticHighlighting.enabled": true,
    "csharp.showOmnisharpLogOnError": true,
    "csharp.suppressBuildAssetsNotification": true,
    "csharp.suppressDotnetInstallWarning": true,
    "csharp.suppressDotnetRestoreNotification": true,
    "csharp.suppressHiddenDiagnostics": false,
    "csharp.suppressProjectJsonWarning": true,
    "csharpextensions.useFileScopedNamespace": true,
    "csharpsortusings.sort.usings.order": "System",
    "cSpell.language": "en-GB",
    "cucumberautocomplete.steps": [
        "IRT.SMF.AutomatedTests/StepDefinitions/**/*Steps.cs",
        "IRT.SMF.AutomatedTests.Shared/StepDefinitions/**/*Steps.cs",
        ], 
    "dotnet.completion.showCompletionItemsFromUnimportedNamespaces": true,
    "dotnet.formatting.organizeImportsOnFormat": true,
    "dotnet.server.useOmnisharp": true,
    "dotnetAcquisitionExtension.enableTelemetry": false,
    "editor.codeActionsOnSave": {
        "source.fixAll": "never",
        "source.fixAll.eslint": "never"
    },
    "editor.formatOnSave": false,
    "editor.formatOnType": false,
    "files.exclude": {
        "**/*.feature.cs": true,
        "IRT.SMF.AutomatedTests/**/bin": true,
        "IRT.SMF.AutomatedTests.ModuleValidation/**/bin": true,
        "**/obj": true,
        ".vs": true,
        "**/Features/IgnoredTests": true
    },
    "folder-path-color.folders": [
            {"path" : "IRT.SMF.AutomatedTests", "color" : "custom1", "symbol" : "AT", "tooltip" : "Automated test project files"},
            {"path" : ".vscode", "color" : "custom4", "symbol" : "VC", "tooltip" : "VSCode configuration files"},
            {"path" : "BatchFiles", "color" : "custom5", "symbol" : "BF", "tooltip" : "Batch files used by custom tasks"},
            {"path" : "ResharperSettingsForPipeline", "color" : "blue", "symbol" : "RS", "tooltip" : "ReSharper settings used by ReSharper pipeline"},
            {"path" : "Documentation", "color" : "cyan", "symbol" : "DC", "tooltip" : "Markdown documents (and associated images)"},
            {"path" : "Pipelines", "color" : "red", "symbol" : "PL", "tooltip" : "Azure DevOp YAML pipeline files (and associated scripts and templates)"},
            {"path" : "ConfigurationFiles", "color" : "magenta", "symbol" : "CF", "tooltip" : "Configuration files used by all test projects"},
            {"path" : "AllureCommandLine", "color" : "custom2", "symbol" : "AL", "tooltip" : "Command line files used to produce Allure report"},
            {"path" : "Packages", "color" : "custom6", "symbol" : "PK", "tooltip" : "AppServerApi NuGet package files"}

    ],
    "gitlens.telemetry.enabled": false,
    "omnisharp.autoStart": true,
    "omnisharp.disableMSBuildDiagnosticWarning": true,
    "omnisharp.enableEditorConfigSupport": true,
    "omnisharp.sdkIncludePrereleases": false,
    "omnisharp.useEditorFormattingSettings": true,
    "omnisharp.useModernNet": true,
    "postman.telemetry.enabled": false,
    "sonarlint.disableTelemetry": true,
    "sqldeveloper.telemetry.enabled": false,
    "telemetry.editStats.enabled": false,
    "telemetry.feedback.enabled": false,
    "workbench.colorCustomizations": {
        "activityBar.background": "#0B4A1D",
        "titleBar.activeBackground": "#0B4A1D",
        "titleBar.activeForeground": "#F0FDF4",
        "titleBar.inactiveBackground": "#0B4A1D",
        "titleBar.inactiveForeground": "#F0FDF4"
    },
}

At present the IntelliSense seems to be working. It started working more consistently when I did another update of the c# extension and disabled most of the c# extensions I had enabled. As IntelliSense had worked before, but then suddenly stopped working for me suggest this issue is kept open for another week or so. If IntelliSense stops working again during that time I will post a comment