Colosseum Map - stuck in arena room after shifting to Nightmare

If you go into one of the arena rooms in the Colosseum Map (based off of A4 Daresso's Dream), and during the wave events, shift into Nightmare, you will get stuck in the arena as no door will open even after all the waves have finished.

I killed all enemies inside the arena in both the regular world and within the Nightmare.

It also seemed like the waves were not coming as fast as I remember, like the game was loading the first wave over and over.

Reference #: 1997261854