A pawn I created keeps jumping up through a floor

So I created a pawn (cube shaped) with a simple AI that follows the player, and your goal is to try to destroy it. I have a spawn point set up for the cubes, and they spawn every second or so. I also built a second floor (just a simple flat box) for you to try and escape to. But whenever I go to the second floor, instead of using the stairs, the cubes seem to just jump up through the floor to get me. I just started using Unreal yesterday, so I have no clue what the problem is. Any help would be highly appreciated. Thanks!