All geometry invisible in all maps on project. How to fix?

Here is what happened:

I opened the project today while I had an unstable internet connection. It loaded unusually slow, and then I noticed the geometry missing. So I closed it and opened it again.

All the geometry in a map is missing in perspective view and in lit. In unlit only very few pieces of geometry show. In player collision view all geometry shows up.

also when switching to any view except of perspective (left right top bottom) then the geometry shows however only on wireframe and collision modes.

This affects every map in the same project. Other projects are not affected.

The project is currently entirely blueprint. However yesterday I clicked on show class which opened a c++ class in vs2022 for view, however I never compiled anything in c++ in this project.

How can I fix that? Is there something messed up with the rendering? Did I change some hidden setting by accident?