I don't have any screenshot or video. The time it happened I didn't think I should post it here so I didn't get any proof.

Me and my friend (both rogue) we were doing duo in arena.
-Stahl appeared.
- spiders spawned.
Ok its cool. We wouldn't move. We would stand opposite side and take the boss out just like other times.
but
- vortex appeared aswel.
it was so tough for us.
As vortex was throwing us from here and there and spiders were spawning.. the arena was full of spiders.

How could two environment overlap and come together?
we somehow managed to do this and killed the boss but isn't it a glitch/bug?