Blazor cannot find variables in related C# class file

I have upgraded my Blazor project from .NET 6 to .NET 8.After I have the issue, that my Blazor componennt cannot see the variables stored in related CS file:

But it is in the related CS file:

If I remove the partial keyword from class definition, it immediately writing error that partial keyword is missing.If I create the variables directly into razor files @code{} block, it immediately writes the variables already defined:

Did any if you already met such issue?

Thanks!G