Help! LOD level1+ all reverted to some random other static mesh?

Weird. Most of my static meshes have replaced level 1+ with an arbitrary static mesh in the project (happens to be a key). Everything in the distance is now a key?

I have started rebuilding LODs manually for each mesh, but I have a lot of them. I tried bulk edit but all I can do was reset a group back to None. Is there any other method for rebuilding all static mesh LOD’s according to their LOD group settings? … without doing 1 by 1.

And why would this happen?