It could simply be a system where you need to fill some category of points up. Like voke perhaps gave 9.9 proc points each, so 10 put you at 99, but you need 100 so the 11th procs. This would then explain why it seems random (you have to do enough moves first)

But I'm just guessing. I haven't even entered Dynamis since the changes. If people proc on early moves, it could be something else (or certain types can get 50 points worth of proc points and quickly proc)