As have I, unfortunately, I'm unclear as to how long this bug will take to fix but it starting to become extremely annoying. I don't know why, but I think it has something to do with the Logan Thackery NPC. What was odd about it is just before the "Hold out as the glory of Tyria tracks Zhaitan” and the previous step where you have to clear out the towers for the ground team, the Logan NPC is still present despite him "sacrificing himself" when we needed to get the power cores. Perhaps that might be issue alongside the NPC's not triggering to help in fending off the various assaults from Zhaitan and only come when the enemy AI is close by.