I have been constantly observing weird behavior when it comes to monsters, pathing and attack range.
It is especially noticeable when playing Minstrel, when my pet gets the aggro, I can melee a monster for 1 hit, and then suddenly the monster is out of range despite the model and myself not moving at all.
I am now observing it while playing Necro, where my pet has aggro, I face the monster to cast the instant lifetap and the monsters consistently run BEHIND my pet, then teleport back in front of it. (My /face will actually jump between two spots)
I believe this behavior also causes the various melee-range issues we have seen reported (one report by @Catkain - Grandfather of Skalds I believe), where monsters were in range and without the model moving, they suddenly aren't.
I can reproduce this issue consistently with Necromancer on basically every pull.