Reproduction steps:
1. Open the attached project
2. Open the Assets folder in File Explorer/cmd/bash
3. Rename folder a to b and a.meta to b.meta
4. Delete a.cs & a.cs.meta from the renamed folder
5. If you restart Unity, it will throw this warning "Timestamps (25) and assets (19) maps out of sync" and a few errors saying that file is in in timestamps but is not known in guidmapper
6. If instead of restarting you attempt to rename folder b/ from inside the editor, it will crash