Whenever I am hosting a cooperative game, friends who join me become unable to move their character when hit by the explosion of any barrel (any damage type). We tested this with all barrel types we could find, we also tested that it did not matter how the barrel was ignited before hitting the player.

The only way to resolve this was to have players leave the game, turn the character to a bot and then rejoin. However the issue would occur again. 

We also had one issue in the same game where the player was frozen in place after taking acid breath damage from the Bug Mumma boss.