I’ve occurred this twice when trying to load an older save while in-game during a current save.
I don’t know what caused this but I usually encounter it when trying to load an older save because something unfavorable happened in-game(a character died, or just re-trying a settler joining the village).
Mods in use:
- Anorien biome
- patrol
- smart crafter
All mods are up to date. Unless they’re not working with current Alpha 17.
Update:
Also just got the same problem when trying to quit to main menu from in-game.