Could not load content for githubusercontent

[Vizual-Dev]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Since upgrading to Visual Studio 2026 and .NET 10 I have started to receive a number of "Could not load content..." errors in the browser.

For example:

Could not load content for https://raw.githubusercontent.com/dotnet/runtime/b0f34d51fccc69fd334253924abd8d6853fad7aa/src/mono/browser/runtime/debug.ts (HTTP error: status code 404, net::ERR_HTTP_RESPONSE_CODE_FAILURE)

The Sources tab in the browser shows:

I have tried cleareing the cache and done a hard refresh, updating the .NET workloads, and even installed the .NET 10.0 WebAssembly Build Tools but I still receive the errors.

Is it possible I have missed a step in the upgrade?

Expected Behavior

No response

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

No response

Anything else?

No response

[dotnet-policy-service]

Tagging subscribers to 'arch-wasm': @lewing, @pavelsavara
See info in area-owners.md if you want to be subscribed.

[dave-gcv]

I am also experiencing this error after upgrading a Blazor project from .NET9 to .NET10.

The effect it has is when i'm starting the Blazor App (Server + Client) in debug mode via Visual Studio it's taking ages for the app to load. It eventually becomes responsive after the request to debug.ts fails.

What I find odd however is that if I create a brand new Blazor project (Auto render mode) this request never gets called - there is no reference to any raw.githubusercontent.com content at all.

This makes me think there's a missing step in the upgrade process

[jeffputz]

Same, and because the OP didn't explicitly say it, this is for debugging .net10 Blazor.

[akoeplinger]

This is because we switched to building .NET inside of the VMR repo (https://github.com/dotnet/dotnet) in .NET 10 and so this URL for the source map needs to be updated:

runtime/src/mono/browser/runtime/rollup.config.js

Line 134 in 928eb5f

res = `https://raw.githubusercontent.com/dotnet/runtime/${gitHash}/${relativeSourcePath}`;

[pavelsavara]

And this one too

runtime/src/native/rollup.config.plugins.js

Line 148 in 928eb5f

res = `https://raw.githubusercontent.com/dotnet/runtime/${gitHash}/${relativeSourcePath}`;