I remember I was complaining about it last year and it was a relatively minor issue then but having player ghosts makes it feel like cheating now
I autoexplored the whole level and searched a corpse. A very dangerous summoner appeared (Emit Sparks on Tower:1!) so I ordered all my demons to kill a single enemy demon, retreated to heal (no items used and I have free summon/unsummon to make it really safe), then returned, repeated it again to kill second demon, retreated again, healed again and so on. Having a cleared level helps a lot, I manually traveled like 30 tiles before those demons stopped chasing me. Not sure how to fix it, generating more demons for multiple retreats from the same summoner maybe? Or restoring fallen demons of the summoner?