Hello! If the problem is what I think it is, then I'm sorry to say that it's not something that can be easily fixed: it's a widely-known issue Renpy has with certain setups for no discernible reason. You'll likely experience the same issue playing through other FVNs made with the same engine.
My only suggestion is to play the game on another device, such as a phone or tablet, and hope it works. I'm sorry to hear you're experiencing this issue, and I hope that this problem can one day be sorted out.