Character getting stuck on flat surfaces with fully build NavMesh

My enemy character gets stuck on seemingly arbitrary, but none the less consistent points on a NavMesh which is build properly (or as far as I know).

Below is a tweet of mine with an animation illustrating the situation.

#gamedev #indiedev #indiegamedev #MadeWithUnreal #UE4 Navigation Mesh problems @UnrealEngine. Stuck on flat surface.

— Alisa Dolinsky (@Alisaxy_) April 17, 2016

I have no clue as to what’s going on. I’ve tried resetting the navigation settings to defaults, playing with the dimensions of the character’s capsule and I’ve already disabled any collisions on its mesh.

Behavior Tree was the problem. I’ve made a simple Behavior Tree implementation and it fixed the navigation issues. I don’t like the vanilla BT anyway: too many moving parts.