I was facing the same issue. I also managed to make a recording of it (was running with a bow at the time), but I can't seem to find an upload-button. From what I noticed the issue was reproducible only on some bats, and also with skills which need to be targeted, so AoE or "auto-targeted"/homing skills or attacks would be able to damage them. The hit-box on them was also really weird (very small, only a few pixels), and even if managing to hover over then an pressing the auto-attack skill, it would still not connect with the bats (SHIFT-attacking in their direction also did nothing).

P.S.: would be glad to provide videos, but I don't really see how to upload them here.

Same issue on bats. As melee was a pain, aoe attacks work but single target very often miss like the mobs non-targetable. Happens with mobs that collapse and repair in Anakis as well. I'll be doing default staff attack to them, they drop and then I can no longer damage them when they hit the ground, then I switch to aoe lightning, and they die. Almost like the single target attack is going after a hitbox that disappears for flying or prone targets. Sucks, but not game breaking like so many other things right now.