This quest is simply broken right now. I couldn't complete it in any of my playthroughs, and it seems like a matter of luck right now

Larian's Biggest Oversight, what to do about it, and My personal review of BG3 EA
"74.85% of you stood with the Tieflings, and 25.15% of you sided with Minthara. Good outweighs evil, it seems."