Razor tools are crashing in VS 2026

[MarvinKlein1508]

I’m opening this issue after a brief conversation with @danroth27.

I’m consistently running into problems with the Razor tools in Visual Studio, and I can reproduce them every single time.

Whenever I switch branches in a fairly large project, I receive the following error message:

When I click Reload, all syntax highlighting for Razor components disappears:

After a few minutes, the tooling may start working again, work only partially, or not recover at all—forcing me to restart Visual Studio. When the green squiggly lines begin to appear, it’s usually a sign that I’ll need to restart Visual Studio to continue working.

I can reproduce it constantly by following this steps:

1. Clone https://github.com/microsoft/fluentui-blazor
2. Switch to the dev-v5 branch in VS
3. Select the solution file
4. Wait a few seconds

I believe this has something todo with the internal git tools as this is also happening sometimes when I revert a lot of changes in the active branch.

[davidwengier]

@MarvinKlein1508 are you on Insiders or stable?

[MarvinKlein1508]

@davidwengier sorry I forgot to mention. Right now I'm using VS 18.2. But I can try on Insiders tomorrow as well. But I will take a guess and say it's most likely the exact same behavior. I will also provide a small screen capture tomorrow.

[chsienki]

@MarvinKlein1508 I'm trying to reproduce this. To confirm when you say 'switch branch' you mean via git on the command line and not using the branch selector in VS, right?

[davidwengier]

@MarvinKlein1508 unless you've turned on the cohosting feature flag in 18.2, then I would hope that insiders is better, yes. In particular, the green squiggles are a result of flaky "tag helper discovery" which is entirely specific to non-cohosting.

Very keen to see how you go with Insiders, but like Chris, I'll try it out myself too.

[MarvinKlein1508]

@chsienki branch selector on the bottom or here:

[MarvinKlein1508]

@davidwengier I've downloaded Insiders on my home pc and I'm getting some kind of different behavior here.
I still get the crash on top (ignore the first error this is because the switch from SLN to SLNX)

But when I click reload this time it automatically closes all my open files (at least it's working then when I open them again).

[MarvinKlein1508]

Nevermind even after opening the files again the editor isn't working reliable

[MarvinKlein1508]

And for confirmation co-hosting is enabled

[davidwengier]

@MarvinKlein1508 if you look in the bottom left of VS, do you see a little exclamation mark? eg.

I just tried to repro this and had no issues swapping from dev to dev-v5, but when I swapped back to dev I got the exclamation mark and when clicking, I see that message about the language server. That specific issue is a VS platform bug, tracked internally as https://devdiv.visualstudio.com/DevDiv/_workitems/edit/2613011 (/cc @kayle), which we're sadly still waiting on a fix for, but it would explain Razor not working. It would also affect C# diagnostics, which might be something else interesting to test - eg, after things are broken, if you open a C# file and put in an obvious error, do you see squiggles? I do not right now:

[MarvinKlein1508]

@davidwengier I have left open the VS instance over night and yes I can see this in the bottom.

However C# is just working fine for me. Only razor has stopped working.

[davidwengier]

I would expect C# to work fine, except squiggles and error list, but either way, the screenshot confirms the issue you're running in to, so that you very much for that.