I did not find any other mention of this issue. I completed this quest successfully last night, playing solo. Today while on an alt and in a party with my wife's character, the quest bugged out for her after we encountered the elder spirit, and witnessed Darien and "Gabrielle" across the way. I immediately got the quest prompt "Talk to the Xul-Haj Spirit" but the quest marker never appeared for my wife's character. She had the same scene with Darien and the spirit said the same lines right after, but then nothing. We abandoned the quest and restarted it and the same thing happened. Quest works for me but not for her. Thank you for your attention!