HELP - Cruel Act 3 Large Soul Core Quest Bugged, preventing progression

I killed Jiquani in Jiquani's Sanctum. He dropped the large core. I got the quest completion. I went back to NORMAL difficulty, same spot in questline to kill a different boss in same map to get the +10 fire res. Killed Jiquani again. Accidentally dropped the first soul core that I got in cruel difficulty.

Went back to cruel difficulty - but now the stone altar is bugged. The quest says to go back to infested barrens and activate the stone altar, but when I do, I get the animation but then the core disappears and the waterway doesn't clear. So I'm stuck.

HELP. I've tried rekilling Jiquani in both normal and cruel, but the soul core won't drop again. I tried resetting the instances on the maps. Nothing has worked. Is there a way to reset the questline?

I have the exact same problem, my character is now bricked..

Same problem here. Have you tried doing coop with someone and trying to make the other player put the stone for you? I want to try but my friends are not there yet