ok, that one definitely is because of RenPy upgrade. not even I can deny that. even if I'm still convinced that all the previous errors with opacity slider and type errors weren't caused by RenPy upgrade. or at least could've been fixed without downgrading
0.7 uses 7.4. 0.8 uses 7.6/8.1.in 7.5 Tom added this stuff that signs the saves so that if you're loading a save from the internet it gives you this popup
if it's the first time you're launching the game using 7.5, it will sign all the saves that are currently in the AppData so old saves will load fine. but if you already have saves that are signed (you will after you launched 0.8), it won't sign any new unsigned saves. and 0.7 can't sign saves because it's using 7.4. so, you have 3 options
1. make an update for 0.7 with new RenPy
2. I wrote some code that signs the saves that were made with RenPy 7.4 and lower every time the game is launched. you probably want to figure out how to make it sign only unsigned saves.
this file
3. downgrade RenPy again to 7.4, now that's just bullshit in my opinion, that's like getting non-stoner FrAnS after you had SAndrA