If I'm right, I think they're having some troubles with how renpy handles rendering some images in older graphic cards on windows. It happens with a lot of VNs and I suspect it has to do with WEBM format (absolutely not sure tho, only a guess). I usually start the game and hold SHIFT + G to open a config panel then change the renderer to Force ANGLE2. After that just need to restart the game.
It's been working just fine for any VNs with similar problems I played until now.