Weight/Gear Problem

I had encountered a problem that I never really had experienced during my state competition a few days ago. My team member and I were using a lift that we had built for our robot to raise our claw (attached to the lift) in order to knock down the stars in our STARSTRUCK competition. However, one of the gears in our gear ratio had slipped out of one of the other gears’ teeth. I am not quite sure what might of caused this because I’m pretty sure all of our pieces were tightened so that nothing would slip (especially the collars, not sure if I spelled that right).

Someone please help :

Did the gear slip horizontally or vertically (i.e. skipping or slid out of alignment)? If it moved horizontally it is because the shaft collar was not properly tightened. To prevent this I would recommend clamping shaft collars or use spacers with the shaft collar.

Thanks guys, I really appreciate your responses!