This feels like user error cause i never have this problem, based on this video it seems like this is a very specific case.
Stalls or grinds are triggered by basically power sliding. You cannot do this if crouched for an ollie which prewind requires. So, of this is happening it's probably cause you're doing the pre-wind AND ollie as you reach the coping instead of before. So, you might be triggering a slide instead of a pre-wind but can't tell since the input is so fast.
The pre-wind is not really designed to be triggered frame perfect on the coping, you can hold it before then.
To me this just sounds like you're trying to very quickly do an input and failing sometimes. Like I do a lot of prewind with flips, which requires input as soon as you get air, but it is possible to do, but doesn't seem explicitly designed to allow it.
