.NET 10 Blazor navigation from wasm to interactive server broken

[AksTheNerd]

Describe the bug

Error when navigating from "@rendermode InteractiveWebAssembly" page via Nav menu with href to a page which has @rendermode InteractiveServer Set.

Uncaught (in promise) TypeError: Cannot read properties of null (reading 'insertBefore')
at q (blazor.web.j8lzlu28q6.js:1:22605)
at blazor.web.j8lzlu28q6.js:1:182422
at li (blazor.web.j8lzlu28q6.js:1:182431)
at si (blazor.web.j8lzlu28q6.js:1:179662)
at ai (blazor.web.j8lzlu28q6.js:1:181600)
at si (blazor.web.j8lzlu28q6.js:1:179225)
at ai (blazor.web.j8lzlu28q6.js:1:181600)
at si (blazor.web.j8lzlu28q6.js:1:179225)
at ai (blazor.web.j8lzlu28q6.js:1:181600)
at si (blazor.web.j8lzlu28q6.js:1:179225)

Expected Behavior

It just works with .net8 and .net9.

Steps To Reproduce

Create a Sample Blazor (Auto) App.

1. Move (or Create) the Home page to the Client project
2. IMPORTANT-> Set @rendermode InteractiveWebAssembly on the Home page
3. IMPORTANT-> Set @rendermode InteractiveServer on the Weather page
4. Start the app and try to navigate to the Weather page from the NAV (via url it works)
   Result: The navigation doesn't work and you get the exception->

Uncaught (in promise) TypeError: Cannot read properties of null (reading 'insertBefore')
at q (blazor.web.j8lzlu28q6.js:1:22605)
at blazor.web.j8lzlu28q6.js:1:182422
at li (blazor.web.j8lzlu28q6.js:1:182431)
at si (blazor.web.j8lzlu28q6.js:1:179662)
at ai (blazor.web.j8lzlu28q6.js:1:181600)
at si (blazor.web.j8lzlu28q6.js:1:179225)
at ai (blazor.web.j8lzlu28q6.js:1:181600)
at si (blazor.web.j8lzlu28q6.js:1:179225)
at ai (blazor.web.j8lzlu28q6.js:1:181600)
at si (blazor.web.j8lzlu28q6.js:1:179225)

Exceptions (if any)

Uncaught (in promise) TypeError: Cannot read properties of null (reading 'insertBefore')
at q (blazor.web.j8lzlu28q6.js:1:22605)
at blazor.web.j8lzlu28q6.js:1:182422
at li (blazor.web.j8lzlu28q6.js:1:182431)
at si (blazor.web.j8lzlu28q6.js:1:179662)
at ai (blazor.web.j8lzlu28q6.js:1:181600)
at si (blazor.web.j8lzlu28q6.js:1:179225)
at ai (blazor.web.j8lzlu28q6.js:1:181600)
at si (blazor.web.j8lzlu28q6.js:1:179225)
at ai (blazor.web.j8lzlu28q6.js:1:181600)
at si (blazor.web.j8lzlu28q6.js:1:179225)

.NET Version

10

Anything else?

No response

[AksTheNerd]

BugReport.zip

[Stuart88]

Seeing the same issue on my InteractiveAuto app.

Last time I encountered this issue it was due to something being disposed while the Blazor DOM still expected it to be there. But by now my app is so large that I have no idea where the problem might be occurring.

Was not an issue with dotnet 9.

[AksTheNerd]

There is a chance it gets fixed if it's fixed with the sample app :)

[PaulHuizer]

I ran into the same issue. Here's a repo with 2 simple identical projects -- one for dotnet 9 and one for dotnet 10:
BlazorApp_Navigation_InsertBefore_Error

Regression: The .NET 9 version works correctly, while the .NET 10 version produces this error:

Impact / current workarounds

This issue affects the navigation flow in our application. A temporary workaround is to force a full reload via NavigationManager.NavigateTo(url, forceLoad: true). This works, but it results in a full engine reload and hydration cycle on each affected navigation, which introduces noticeable overhead.

Another workaround is downgrading back to .NET 9, but ideally we would continue on .NET 10.

Milestone

I see the issue was added to the Backlog milestone. Just to confirm: is this regression already on the team’s radar for a future .NET 10.x servicing update, or is more investigation needed?

Happy to provide additional details or help with further repro steps if needed.

[PaulHuizer]

After further efforts to find the difference between working and problematic pages, I found the following:
If a page does not have a PageTitle tag, it shows in the browsertab localhost:xxx/somename, from that moment on the nav is broken.

workaround III
Add a PageTitle tag: <PageTitle>SomePageName</PageTitle>

PS:
I tried and checked the bugreport.zip from above. It appears to be a different issue.

[Stuart88]

workaround III
Add a PageTitle tag: <PageTitle>SomePageName</PageTitle>

Unfortunately didn't do the trick for me (but did help me find some pages with missing titles!)

[PaulHuizer]

Unfortunately didn't do the trick for me (but did help me find some pages with missing titles!)

It appears to be a completely different issue. I'll create a new issue so the PageTitle issue can be triaged on its own.
Here: aspnetcore issue #64522

[javiercn]

Unfortunately didn't do the trick for me (but did help me find some pages with missing titles!)

It appears to be a completely different issue. I'll create a new issue so the PageTitle issue can be triaged on its own. Here: aspnetcore issue #64522

It's actually the same issue.

There's a PR with a candidate fix:
#64529