At first I thought something might be wrong with the warrior trait Sweet Revenge sometimes not rallying you when you killed an enemy (an actual enemy not an object like a catapult), but it seems like it is rallying itself that sometimes bugs.
I’ve noticed it several times over the last couple weeks, and just died on an alt after killing a lashtail devourer in fields of ruin and didn’t rally.
Hopefully the devs are aware of this and are working on it. It’s getting pretty annoying, especially in the tower of nightmares. (getting downed, killing something and not rallying is a big kick in the balls in that place)