Issues while at school

Been playing High School Years since the day it came out with no issues, even after updating. I removed most of my mods and updated the few I still have. I also replaced the school with one from the gallery. Now, my game completely freezes/lags while at school - specifically during free periods, lunch, and when school ends. I'll try to have my sims do something, and they just stand there frozen until it's time for class. If I try to switch between teens, it takes like 3-5 minutes to actually do so. Once school is over, my sims freeze and stay at the school until like 6 PM when they finally move again. I don't know why this issue is suddenly happening but it's really frustrating because I can't do anything in the school except attend class.

This problem does not occur at any other lot.