Ah... you were probably climbing. Our climbing system works such that if grip button is down and hand connects with a surface, then you will grab it. That way mistimed grabs aren't frustrating to climb with. But, if you play like me and hold grip buttons down when "holding" a gun, it's easy to get caught on stuff. And the first instinct isn't to release grip because you're probably holding a gun.
Could be something else, but I'm guessing that was it because it still happens to me because I white knuckle my controllers lol