Not sure how this happened, but today there were two Banishers and two Walkers on island 5 in sky. (See Screenshots linked below). One of each was static and not moving, the others pathed like normal. I assumed the static one was a ghost at first as sometimes happens with mobs, but they were both very real. I have no clue what caused this or how to fix it, but reporting it for due diligence.
http://s23.postimg.org/ljxakngnf/EQ000135.png
http://s22.postimg.org/gxaj4g02p/EQ000137.png
Edit: there was still one arbiter and one caller, fyi