It's happened again, this time on 2.0.21-5. All five autosaves fail with the same error:
1.600 Info Scenario.cpp:178: Map version 2.0.21-5
2.719 Warning Map.cpp:358: Map loading failed: Corrupt map: unknown entity prototype ID 1896.

Interestingly, a friend was on the server when his computer ...

Thanks for the report however unless you know of a way to take a fresh save file and get it into this state I can only assume some hardware fault broke the save data as it was being written to the zip and to disk. This error means "you have hardware issues or something/someone corrupted the zip ...

I've just experienced the same bug on my server. I launch my game with a script which automatically overwrites the map file with the latest autosave if it is newer and restarts the server if it had a nonzero exit code. While playing, the server crashed for some reason and tried several times to ...