Hey, just wanted to let you now I may know whats going on with this. I have the lagging problem too, with ALL the scenes. I am using linux, so it may not be the only problem, but I think what is going on is that the game is using the CPU, rather than the GPU to render the video. I noticed that when I have the lagging issue, my CPU usage shoots up tremendously, but I have a pretty good graphics card, so it should be using that, and not my CPU. There may be some code or something you need to use to have the game render using the GPU, if a GPU is available.
Not sure if it will be of much help, but there is a forum topic asking about something similar:
https://f95zone.to/threads/solved-f...-on-discrete-gpu-instead-of-integrated.32409/
Edit: I may be using the word render wrong, but hopefully my point gets across. GPUs are great at image stuff, because the specialize in it while CPUs are better for general purpose stuff.
Edit 2: I should also mention that my cpu usage shoots up to 100% It is liely the lag comes from the CPU not being able to handle the video. I have a Intel® Core™ i7-7700HQ CPU @ 2.80GHz × 8