I cleared the zone "Stem Quarry" with my Sawbutcher, before I went to the Sunwall city (and therefore I didn't have the quest "Hunter, Quarry" yet).
After vanquishing High Sun Paladin Aeryn, I received the "Hunter, Quarry" quest - and instead of it completing immediately, I still had the objectives to destroy the 3 steam valves (which I previously did).
So I went to the Steam Quarry, and the first level of the zone was cleared, but the Steam Generator lived again. I went and walked over it, and that finished the first part of the quest.
Upon entering the 2nd level, the whole lever was re-generated and unexplored. The bosses lived again. Same for the 3rd level. So I could walk through and kill the bosses twice.
My character: https://te4.org/characters/30982/tome/2 ... df3a3def44