Invisible collision suddenly appeared

So i’ve almost finished building something, and for some reason there is a big, tilted surface, that is invisible and has collision, and I can seems to figure out what it is and delete it/change it’s collision.
What can I do?

We’ve also encountered this problem in 4.18.2. We’ve searched through the World Outliner but haven’t found any guilty objects. Does anyone have any suggestions for this issue?

After a process of elimination, we discovered that the invisible mesh was attached to a combined static mesh actor. Removing and replacing this (a bunch of large rocks) eliminated the large invisible collision and nav mesh.

I’m not sure that this error with the combined static mesh actor did not exist in 4.17, but 4.18 broke a lot of LODS, so I suspect that it is the culprit.

Thank you very much! I wasted a looot of time trying to figure out what’s going on.
Version 4.24, same problem.