I’ve just tried beating Leviathan in 4 person COOP at OP10, we tried that twice (exited the game in between attempts). Both times it happened same way: after shooting out the eyes, his health stopped going down. Hitting the heart showed damage stats next to the shot impact spot, but his health bar was stuck (see screenshot). We were killing sandworms and shooting the heart over and over again, no change.
Anybody had this happen?