Mobs appear to be spawning in top-left of map

(Windows 10 - 64bit, game version 0.0.18)

I believe I’ve caught glimpses of this in several realms before, but in the attached screenshot, you can see that there appear to be several mobs stuck in the corner. I would assume these were new spawns as I roamed around.

This is normal realm level 48 (post-game) if that helps.