Just wanted to report another problem with coop play, I have encountered several times.

In a coop instance (Liberate the lost) when facing the final boss, if your whole group gets taken out and everybody has used their self-revive and there is nobody left to revive team members, there is no way to exit the instance. The whole group is left crawling around the instance and the only way out is to exit the game completely.

This problem I encounted with the final boss on Liberate the lost but it probably is the case for other coop instances too. There should be access to the menu to allow the group to either restart the whole instance or start at an earlier part of the instance.