I'm not sure which save file it was, because I saved frequently under different numbers. The error seems to be object related, and linked to the lot. I tried to save a bugged lot to my library/gallery without success. It gave no error message, but the lot wasn't in my gallery and the home page news feed showed a whited out picture. It was corrupted and couldn't save. I bulldozed my lot, placed another from the gallery, and the game has played without issue.
FYI: I play with and without mods. The error happened both ways, but recoloured objects are causing major issues with the latest patch. I've seen several 533 errors caused by objects I've played with for several months. I didn't report them, because they are mods and it's my fault for using them.