Terrain, character stops moving

So, this is weird.

I have a terrain, made with UE4 terrain tool, but there’s a bug(?) where, in certain places on the terrain, my first person character stops moving. I can’t move, can’t jump, anything. It’s not on a slope where the character could be stuck. It also never happens when the character is on a simple, flat cube. It’s a slightly modified First Person Character, and I didn’t make any modification for this to happen.

Any ideas?

EDIT Found the problem!