I noticed a quirk in the NPC AI. I fight a particular spawn in some somewhat hilly terrain (because when I fight on flat terrain, my Yagel's mag guns seem to shoot at my feet instead of the enemy). There's one bit of straight-line impassable (due to slope) terrain on the hill between us that's not big, probably 40m wide. A couple times, the AI would get stuck on the other side of this terrain and pace back and forth, the pathfinding unable to recognize it could get around by simply going another 10m in either direction. After pacing back and forth a few times, it would give up and return to it's spawn point. Once there, it would then begin pacing (or shuffling)  back and forth over about 5m, and it'd be stuck. If you approached it, it would lock and fire, but short of putting it out of its misery, it would not stop it's pacing. It wouldn't pursue, try to keep it's optimal, nothing.

I've seen it happen twice, though I suspect it would happen more often if I forced them around this obstacle each time.