download and web versions are exactly the same, so it's weird there are differences. And if you set the framerate to 60 ideally it would need to fix the bug if that was the cause, but since it doesn't I'm really not sure what the cause could be honestly. I'm sorry that this problem came up and ruined the experience for you.
Do you have by chance another pc or laptop you could test it on?
EDIT:also, what browser are you using? This game was designed to be played with Chrome or Firefox, other browsers may not work properly