The solution I proposed earlier, to copy-paste affected actors to a text file for safe keeping, does not actually help: it seems that if they are broken under the hood then they will be copied as such even if everything looks okay from the outside (editor UI, PIE). I was happily producing backups for a while then realized that they contained the same broken actors as the map.
I’m looking at two dozen actors, fundamental to the project, and no way to keep their data safe so I’d really appreciate any ideas for a backup solution.