Did you find the solution? I’m trying to learn UE, a friend of mine share with me a project files with the assets and I have the same situation you described
I open a level map and almost everything is invisible, and a message log says
[Static Mesh Actor] : Static Mesh Actor has NULL StaticMesh property
I didn’t understand what was going on, so reading online i got that the actors are on the map but the meshes were not assigned anymore to them, and doing it manually make them visible but with no materials
also on the content browsers the meshes thumbs appears as they should (with their proper materials) but once I Select them and try to drag to the level, their thumbnail changes as a mesh without material
Did you find how to reassign/reload the meshes and materials?