EDIT: I found a fix - I changed world tiers, and he became clickable again. Quest complete!
The quest is on the step “Speak to Rakhaan”. When in another region, the blue quest marker appears, but when I enter the region in question (the accursed wastes) the marker disappears. Rakhaan’s character model displays, but is not clickable. I cannot progress the quest.
Restarting the game and completing other quests does not fix it.