This is common if you play without NRaas Mods and have the EA bugfest turned on as I used to get them a lot before adding the NRaas Mods to my game and using the NRaas Mod version of story progression in the place of EA's bugfest which was so overactive that it pushed the town over the edge and caused memory leaks.
I've not had any Error12's with my games and likely won't ever see them unless I foolishly overpopulated the town way too fast like EA's glitchy version of"story progression" known as the bugfest always did when I played Mod-free.I also have stopped trying to play long term multi-generational legacies in any EA worlds and only use empty custom worlds for those as I can just start out small and gradually build my town up over the generations.