I'm not able to reproduce.I have no mods. 0.351 is the latest and only version (other than 0.352 ofc) I played and everything was fine
EDIT
Second new save is now working fine. Idk what was the problem.
EDIT 2.
It's laggy again after the first day at school.
Starting new save and playing a week. I can save/load without issue, like less than a second loading time. Rollbacks are instant, I don't understand what could be the issue?
Is the first loading time (at the start) very long too?
There is a lot of debug times in the log.txt at the start of the game for troubleshooting, if it's also long at the start maybe checking it might give a lead.