FWIW, here's what's happened with my game. Last weekend created a new game in Seasons; everything OK (the odd crash, but nothing unmanageable) until I made the husband a self-employed Nectar Maker. Immediately, game crashed frequently and froze or lagged constantly; some Error 12s. Rebooted a couple of times but no change.
Today, I changed the husband back to self-employed angler (which was previous job), no change -- froze immediately and every two to three minutes thereafter -- so went back to City Hall and made him a self-employed Nectar Maker again, and guess what? Now no problems. No freezing/lagging and so far no crashes (although I'm still saving every 5 minutes).
Very strange, but at least I can postpone deinstalling and reinstalling the entire shebang for now.