Treasures of Utzaal Hammer Bug

Not sure if this is happening to everyone, but my friend and I were playing couch mode and got to the Molten Vault boss fight to complete the Treasures of Utzaal mission. We completed the boss fight and got the hammer but when we got back to the encampment, Oswald didn't spawn, even though the mission was saying he should've been in the encampment. After about an hour of trying different things to get him to spawn in home base, I went onto single player on my Monk and all of a sudden, Oswald spawned in. So I completed my quest but when we swapped to his Archer, Oswald still wasn't spawning. I would like to hear any ideas that anyone might have. maybe running back through the dungeon that we got the hammer from would fix it and get his AI to go back to spawn? but I don't know if it would work.

I have exactly the same problem. Have you found a solution?

A portal will appear soon. Oswald will stand nearby and the second player can complete the quest

I have exactly the same problem

Still bugged, repeat it already 5 times