I joined the group with my friend and ended up getting stuck on the “talk to Yulia in Thetima” mission. I can’t complete this mission, in fact the icon doesn’t appear on the NPC’s head to complete it.
This happened to me as well, although with a slightly different condition. I’ve never been in a party with anyone. I completed the campaign until I could go through Temporal Sanctum to get to Act 9, finished the campaign, did monoliths for a while, and now I want to kill Architect Liath for a prophecy, so I went back to Act 5. Once I got to the Liath and Thetima quest, I cannot advance past “Speak with Yulia in Thetima”. I can speak to Yulia, including the quest option, but it does not complete the quest, and there is no portal on the dock. I see a bug report that indicated this should’ve been fixed in 0.9.0f, but it appears it’s not fixed.
Edit: I partied up with someone with Lagon’s Isle waypoint and teleported to them, and it progressed the quest.