Blazor Web App fails to load WebAssembly after publish .NET 10 / VS 26

[mikermnv]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

After publishing a Blazor Web App created with the default template using .NET 10 and Visual Studio 2026, the application starts successfully, but the WebAssembly part fails to initialize, while server-side rendering continues to work as expected.

The project was configured with:

• Interactivity: Auto
• Per Page/Component Interactivity: enabled

This issue occurs only after publishing the application. Running the app via dotnet run during development works correctly. The failure manifests in the browser with multiple runtime errors related to the Mono WASM runtime.

This issue only occurs when using:

• .NET SDK: 10.0.100-rc.2.25502.107
• Visual Studio: 2026 (18.0.11111.16)

The same project works without issues when published using:

• .NET: 9
• Visual Studio: 2022
  No code or configuration changes were made between versions — only the SDK and IDE were updated.

Expected Behavior

After publishing and launching the app, both the server-side and WebAssembly parts should work correctly. The WASM runtime should load in the browser without errors, just like it does during development.

Steps To Reproduce

Project Setup

1. Create a new Blazor Web App using the default template in Visual Studio 2026.
2. Choose .NET 10 as the target framework.
3. Leave Interactivity set to "Auto" and "Per Page/Component" (default).
4. Do not modify any code or configuration.

Publish and Run

5. Publish the app using default settings:
   • Configuration: Release
   • Target Framework: net10.0
   • Target Runtime: Portable

6. Run the generated .exe from the publish folder.
7. Open the browser and observe that the WebAssembly part fails to load, while the server-side rendering works.
8. Check the browser console for runtime errors.

Exceptions (if any)

Click to expand browser console error output

dotnet.runtime.fn94ls2wwa.js:3 [MONO] * Assertion at /__w/1/s/src/runtime/src/mono/mono/metadata/assembly.c:2718, condition `' not met

MONO_WASM: mono_wasm_load_runtime () failed [object Object]

dotnet.wyqvhxwscv.js:4 Uncaught (in promise) ExitStatus {name: 'ExitStatus', message: 'Program terminated with exit(1)', status: 1, silent: true}

dotnet.runtime.fn94ls2wwa.js:3 Uncaught (in promise) ExitStatus {name: 'ExitStatus', message: 'Program terminated with exit(1)', status: 1, silent: true}

blazor.web.911ktl676v.js:1 Uncaught (in promise) ExitStatus {name: 'ExitStatus', message: 'Program terminated with exit(1)', status: 1, silent: true}

.NET Version

10.0.100-rc.2.25502.107

Anything else?

.NET SDK and Runtime Info

.NET SDK:
Version: 10.0.100-rc.2.25502.107
Commit: 89c8f6a112
Workload version: 10.0.100-rc.2.25513.4
MSBuild version: 18.0.0-preview-25502-107+89c8f6a11

Runtime Environment:
OS Name: Windows
OS Version: 10.0.26100
OS Platform: Windows
RID: win-x64
Base Path: C:\Program Files\dotnet\sdk\10.0.100-rc.2.25502.107\

.NET workloads installed:
[android]
Installation Source: SDK 10.0.100-rc.2, VS 17.14.36603.0, VS 18.0.11111.16
Manifest Version: 36.0.0-rc.2.332/10.0.100-rc.2
Manifest Path: C:\Program Files\dotnet\sdk-manifests\10.0.100-rc.2\microsoft.net.sdk.android\36.0.0-rc.2.332\WorkloadManifest.json
Install Type: Msi

[ios]
Installation Source: SDK 10.0.100-rc.2, VS 17.14.36603.0, VS 18.0.11111.16
Manifest Version: 26.0.10970-net10-rc.2/10.0.100-rc.2
Manifest Path: C:\Program Files\dotnet\sdk-manifests\10.0.100-rc.2\microsoft.net.sdk.ios\26.0.10970-net10-rc.2\WorkloadManifest.json
Install Type: Msi

[maccatalyst]
Installation Source: SDK 10.0.100-rc.2, VS 17.14.36603.0, VS 18.0.11111.16
Manifest Version: 26.0.10970-net10-rc.2/10.0.100-rc.2
Manifest Path: C:\Program Files\dotnet\sdk-manifests\10.0.100-rc.2\microsoft.net.sdk.maccatalyst\26.0.10970-net10-rc.2\WorkloadManifest.json
Install Type: Msi

[maui-windows]
Installation Source: SDK 10.0.100-rc.2, VS 17.14.36603.0, VS 18.0.11111.16
Manifest Version: 10.0.0-rc.2.25504.7/10.0.100-rc.2
Manifest Path: C:\Program Files\dotnet\sdk-manifests\10.0.100-rc.2\microsoft.net.sdk.maui\10.0.0-rc.2.25504.7\WorkloadManifest.json
Install Type: Msi

[wasm-tools]
Installation Source: SDK 10.0.100-rc.2, VS 18.0.11111.16
Manifest Version: 10.0.100-rc.2.25502.107/10.0.100-rc.2
Manifest Path: C:\Program Files\dotnet\sdk-manifests\10.0.100-rc.2\microsoft.net.workload.mono.toolchain.current\10.0.100-rc.2.25502.107\WorkloadManifest.json
Install Type: Msi

[wasm-tools-net9]
Installation Source: SDK 10.0.100-rc.2, VS 18.0.11111.16
Manifest Version: 10.0.100-rc.2.25502.107/10.0.100-rc.2
Manifest Path: C:\Program Files\dotnet\sdk-manifests\10.0.100-rc.2\microsoft.net.workload.mono.toolchain.net9\10.0.100-rc.2.25502.107\WorkloadManifest.json
Install Type: Msi

Configured to use workload sets when installing new manifests.

Host:
Version: 10.0.0-rc.2.25502.107
Architecture: x64
Commit: 89c8f6a112

.NET SDKs installed:
9.0.306 [C:\Program Files\dotnet\sdk]
10.0.100-rc.1.25451.107 [C:\Program Files\dotnet\sdk]
10.0.100-rc.2.25502.107 [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 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.21 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.10 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 10.0.0-rc.2.25502.107 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.21 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.10 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 10.0.0-rc.2.25502.107 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.21 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 9.0.10 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 10.0.0-rc.2.25502.107 [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

[MihuBot]

I'm a bot. Here are possible related and/or duplicate issues (I may be wrong):

• There are some errors "MONO_WASM: mono_wasm_load_runtime () failed" when go to the Counter page after publish the Blazor WebAssembly app #63970
• After installing 10.0 RTM, publish 9.0 Blazor WebAssembly app, some errors "MONO_WASM: mono_wasm_load_runtime () failed" appears when go to the Counter page #64049
• .NET 10 rc2 Blazor WebAssembly app does not work on Azure App Services #64041

[javiercn]

@mikermnv thanks for contacting us.

This is a dupe of #63970 which I believe is getting fixed for RTM