i found a reddit thread where someone explained his issue was from a "surviving" hellfire watcher with 2 hp from the steel foundry (before he exploded it). He had to go back, find it and kill it using telekinesis and it fixed his issue.
I had the same loading crash at 33% so i went back to my save before blowing it up as well, and lo and behold i found a 1 hp watcher that didnt fully die. Did TK and it fixed it.
Highly suggest and see if others can see if this fixes it.
Sucks because i have to redo Janneths quest, wyrmway and gortash, but i suppose its better than restarting further back
