In my case, they just keep running around me, sometimes to end up running in place forever (from 30 to 50 fps).
I once got to a scene while clearing a wave, somehow, but that's the one and only time i'll see it, apparently.
The past month another user said that there is an update that is supposed to allow to view h scene even for people like us with crappy pc/low fps.
Sadly I can't find that update anywhere, so I can't confirm if it work or not.
I really hope that one day I will be able to play the game while seeing the h scenes. I love everything about this game, I'm so mad that I still can't view a single goddamn h scene.