Missing Plugin/Puzzle Piece/Yellow Triangle FCPX

Had this problem myself. I searched the chats, but nobody ever found the answer. Ended up finding a solution myself, so in-case someone comes looking again, here it is.

Problem: Not enough space left on SSD while saving project, so the export was interrupted. This corrupted the proxy/optimized media, resulting in the “missing plugin” warning icon. I couldn’t even re-import new files of the same clips of footage. And replacing the corrupted proxy didn’t help either.

Solution: In the end, I just copied and pasted the whole project into a new library, and it fixed itself. It was a small project, so it wasn’t much trouble. This will be more of an inconvenience for larger projects, but it did solve my problem. Hope this helps!