the first two hits can't crit, you know?
Anyway, about the original topic:
It requires more testing. The only real smash that I can think of that would be affected by this would be Invisible Loom, where the first hit would crit them out. No other scenarios make sense. It MAY be that sometimes you send the monster flying so freaking far that you can't even use your finisher, but I doubt that's the real problem. Unless you use the 4 hit smash on trash mobs a lot, I see no problem with crit.
But, again, more testing D:
I'm pretty sure the lift up motion of the smash of quake hell can crit, I've had it happen to me before.
It happens to quake hell too if it's on the edge of it because they get knocked to the side; thus, not getting hit by main, floor cracking part of the smash