currently unable to speak with lady Prestor regarding onxyia chain quest.
Not a bug, someone else is doing the quest, wait for that to be over
actually it is a bug I think. I had the same issue too. And had to get it the next day. At first i thought it was a bad respawn, and maybe it is but after watching the event happen twice and her respawn I still was unable to talk with her after it was all over.