Hi,
if a player has problems hitting a fill at the correct time, you just go into style record mode, choose the fill causing the problem, change Cue 2 from "immediate" to " next measure, first measure". Write to user style.
Doesn't matter when you hit the fill then, it won't trigger till the begginning of the next bar, no glitches if you hit the fill at the wrong time.

Personally haven't really had any hassles with the fills.

best wishes
Rikki