I forgot to screenshot this, but i did some type of combination of my keyboard, and paused the game. When i resumed litterally HALF of all units that spawned in, including bosses did not come throught the wall barrier. The couldnt attack me, nor approach me, so as it did make it kind of easier to kill bosses, it made it a little harder, it also felt like they glitched in and then i got swarmed by more things than i was supposed to.
SHORT SUMMARY
All creatures and bosses could not get into the main arena, from some glitch i did. I think you need to fix how they spawn, so you can stop things from landing outside the barrier, and to prevent this from happening again.
Also only the reaper boss could get through, because it teleports.