season 1 moved smoothly tho, still does
Maybe check your system performance with task manager in both seasons animations, if it is already near the limits of performance in season 1 but still runs smoothly enough, maybe with a different Renpy version on season 2 it requires a bit more of your hardware and doesn't run so smooth. It runs smooth on both seasons for me and my PC is like 3+ yo on the most important parts (CPU/GPU) and only 16GB RAM. I go check if what ask of it on both seasons is different just to get an idea.
EDIT : I just checked my performances in both seasons, in my machine season 1 most cutscenes and sex scenes animations pushed my CPU between 7% min 14% max and GPU most between 19-23% and a few no idea why 33-37%. But in season 2 it pushes much more on the CPU, I got values of 20 up to 45% in plenty of them and it was almost always 30%++ so probably it is pushing too much your CPU and isn't handling it, GPU values were always between 24-28% and were steady in all of them not like in season 1. But yeah season 2 pushes much more from our CPU's.
EDIT2 : If the problem is CPU usage then you can find good tips on the web if you google search by "how can i solve cpu performance playing animations or videos", but a few are basic like updating windows (if is windows you are using) and drivers and turn off start up programs like things that run automatically once the OS "loads" (I always have the minimum running once my W11 starts ), close background programs/apps etc etc.