Locked in Boss Battle Arena (Burial Bog T8)

I just ran Burial Bog T8 map. I entered the area with the boss and defeated him.

When I tried to leave the area to explore the rest of the map, it wouldn't let me.

There was a reddish shield and one of the orange door symbols that said 'Arena' but I couldn't click on it and couldn't leave the area. I could portal back to my hideout but when I returned it was the same issue.