I was doing the Zerith-Var quest with a friend, and during the part where Zerith creates a portal leading to Khenarthi's Roost, the portal was created for my friend but not for me. Strangely, the quest is marked at this part in Khenarthi's with the text "Enter the portal," but there is no portal.

I'll restart the quest, but I believe this should be looked into!

The map mark:


The quest stage:


@ZOS_Kevin