Odd behavior in multiplayer in Lightless Passage

Repro conditions:
1. Load into an instance of Lightless Passage in multiplayer. 3-4 players used here.
2. Have 1 player exit the game.
3. Have the rest finish the map, and get through to the end.
4. Everyone else exits.
5. Player that initially left logs back in. (This was days later for us)
6. Other players join him.

Results : All the other players still have full map completion of the zone.
Not ... really sure if this is a bug, but it was pretty weird.

And then additionally.
7. Have everyone wait around for like 2 hours.

Results : Several enemies AI just kind of breaks. The rare special snake enemies will get stuck mid-attack animation which makes them invincible for a while. Also the big abyss circle will already be active before anyone approaches it.

This is for PoE 2 btw, Couldn't find another place to put ones specific for that.