Steps to reproduce :
Pretty sure you can figure it out by the picture but :
Take the elevator down, walk a bit and during a horde watch the rats coming from tome 2 boat stairs right to you.
I thought rats hated water
Edit : Sorry for not mentioning this before but I m running on the “big beta update” version.
Supplying a few more screenshots, happens with every enemy, even got grabbed by a packmaster walking on the water while jumping down for the tome which instantly killed me and dropped the tome in the water