Blazor after Visual Studio update throws some strange JS warnings

After updating Visual Studio to 17.11.3, in almost every file that I opened with Visual Studio threw some warning:

Severity    Code    Description Project File    Line    Suppression StateWarning (active)    TS1109  (JS) Expression expected.   Miscellaneous   D:\xxx\Components\Core\DialogConfirmComponent.razor__virtual.html__virtual.js   9   

As on screen

Is it some .net bug, or I should do something with it? I have no idea what this is: _virtual.html_virtual.js; I guess some temp file?

Before the update there was no such things.

Edit

Minimal reproducible example:

0. Have 17.11.3 Visual Studio
1. Dotnet new install MudBlazor.Templates
2. New project - MudBlazor Web APP (server rendering mode / global)
3. Open counter component, delete all.
4. Paste into this counter component

<MudButton Variant="Variant.Filled" Color="Color.Primary" DropShadow="false" OnClick="@(()=>blabla())">Validate</MudButton>@code {    public void blabla()    {    }}

5. Save and see the warnings