Balbala boss fight causes all monsters in zone to respawn

This seems to be consistent for me. I fight Balbala, defeat her without dying, respawning at checkpoint, or portalling out. When I leave the arena, all the monsters I'd previously killed are alive again.

I didn't notice it at the time, but I definitely can agree to this as I had cleared pretty much all of the map, fought Balbala and then had tons of spiders in areas I'd purged.

This clears up the confusion I had about "How the hell are there so many spiders in this damned passage I cleared?!"

Bug Report ID: #3354825106

Had a similar issue, and here's the steps I took to get here:

1) Clear half of traitor's passage
2) Defeat Balbala, no deaths
3) Teleport to caravan to talk to NPC
4) Travel to Trial of the Sekhemas, talk with Balbala
5) Do NOT start a Trial
6) Teleport back to Caravan
7) Stash some things
8) Waypoint to Traitor's Passage, same instance with map half revealed
9) Teleport to checkpoint outside Balbala's boss arena
10) Teleport to the checkpoint near that dead-end where the gold coins are strewn out and there's a treasure chest (I had already killed the spiders triggered by this area)
11) Return to Balbala arena -- spiders. spiders EVERYWHERE.

Other enemies like skeletons or golems all seem to stay dead, and their corpses are still littering the field, plus map is still revealed, so I know for a fact it's the same instance but now every room I go to is spawning spider encounters on seemingly every possible spawning zone. Often multiple times per screen - ex: the small ones that rappel down on their webs, the bigger ones that crawl in from off-screen, both, or multiple of the same types.

Also, for what it's worth, I haven't changed gear or passives or leveled up since leaving and coming back to this instance, and yet all the spiders are consistently stronger than the ones I had killed up until this point. And many packs are Magic or Rare. At first I thought both of these were flukes, but I'm talking like 3 rares and two magic packs in adjacent rooms back-to-back. I haven't encountered anything like this in all the campaign instances yet at about 20 hours in so what are the literal odds?

--edit--

I spawned one pack that had 2 rares in it on my way out of the dungeon btw.

And it's worth noting that I did this quest before on another character and the spiders did not respawn when I left and came back, but the only difference is I beat the boss after clearing everything else, and so I only teleported back to pick up some loot and then leave to go to the next area.