The localization thing is an issue…
If you auto localized on the old level or the project with the level you switched, that could explain these errors and the localization needs updating or replacing.
I also read the autolocalization can affect textures with words on them or some internal naming that needs it.
Maybe a Build Localization could help…
I’ve also been considering the snapshot situation, if not all files are accounted for or even mild HD corruption, moving the entire project folder elsewhere before syncing to a previous snapshot, would give a totally fresh folder just in case something has been left over.
I wonder if making a snapshot, moving project files then downloading the snapshot would clear anything ?