Bug Report ID: #560569258

Here's what happened:
I was fighting the Cortex boss.
I received a trade offer.
I invited the player to my party.
I entered my hideout to complete the trade.
Upon returning to the boss room, it was completely empty. The boss and the portal back to the map had disappeared.

I've attached a screenshot that shows the portal is missing in the boss room but it is still visible on my map (hovering over the minimap)
https://drive.google.com/file/d/10LQ82yMOz529OKzILw_YATj3MquxVorT/view?usp=sharing

This is by design. Was changed years ago so someone must be in the instance when loot is generated otherwise no loot generates. This applies to 5-ways, Cortex, and a few other instances where loot generates after some time.