Editor not working after Visual Studio 18.4.0 update

[julealgon]

I immediately stopped getting any handling on .props files after opening Visual Studio after just having updated it to version 18.4.0 today.

The files open with zero highlighting:

Same behavior observed in other file types, such as csproj:

[espenrl]

• Visual Studio 2026 Community Insiders [11605.296] (March 2026)
• Visual Studio as Arm64 native process (Windows on ARM)

I'm experiencing the same for all MSBuild files. The features are not working, no colorization, no auto-complete.

The following exception is shown at startup

System.ArgumentException: Failed to get the editor factory manager for 4c9bc7a2-907a-44aa-99ea-d1b57b1a20f8.
   at Microsoft.VisualStudio.PlatformUI.Packages.ShellService.EditorFactories.EditorFactoryRegistrar.<GetMatchingEditorFactoryAsync>d__12.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.VisualStudio.Platform.WindowManagement.WindowFrame.<>c__DisplayClass86_0.<<CreateEditorInstanceAsync>g__GetEditorFactoryAsync|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.VisualStudio.Platform.WindowManagement.WindowFrame.<CreateEditorInstanceAsync>d__86.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.VisualStudio.Platform.WindowManagement.WindowFrame.<LoadDocumentFrameInternalAsync>d__85.MoveNext()

It's related to MSBuild Editor as I found the guid in the source code.

MonoDevelop.MSBuildEditor/MonoDevelop.MSBuild.Editor.VisualStudio/PackageConsts.cs

Line 14 in c77880a

public const string EditorFactoryGuid = "4C9BC7A2-907A-44AA-99EA-D1B57B1A20F8";

Even though the editor seems to be registered.

NOTE: I'm also using ReSharper though it doesn't change anything when I disable ReSharper.

[espenrl]

Seems to be an issue with loading assemblies. Log output from devenv /log

ActivityLog.xml

[espenrl]

Seems like the logic behind IntrinsicFunctions have diverged between MSBuild and the replicated logic in this repository. But I'm not entirely sure. See https://github.com/dotnet/msbuild/commits/337c1237984c11add49298f8682b1ab1a3a7db12/src/Build/Evaluation/Expander/WellKnownFunctions.cs