I get this now with a new solution: errors all over the place, but I can compile without problems.
Tried invalidating caches and restart multiple times, same problem. Also Clean, etc… nothing works.
Rider even seems to think that all the test nuget packages from Microsoft don't work or something.
See the screenshot attached (had to sanitize it for NDA reasons):
Edit: even tried to delete the project locally and checking it out again from our gitlab, still the same problem.