I have been using Visual Studio 2019 with Resharper. After last Visual Studio update I had to also reinstall Resharper. However, now VS functionality in some files doesn't work(Yes, VS functionality in some files working correctly, but in others not).
Here is the list of problems I noticed:

Info:
I tried to fix/reinstall Visual Studio and Resharper, not fixed the problem. Visual Studio works fine If I disable Resharper
The only solution for me was updating Resharper to 2021.1.3 (Connor Stoop mentioned in comments)
2021.1.5 version is released which fixes the problem.
This is also happening to me with Visual Studio 2019 16.10.3 and ReShaper Ultimate 2021.1.4, I'm seeing the problem
Workarounds are: