As other have said, this is a Legion client issue and is incredibly annoying when tanking groups. In an ironic bit considering the targetting issue, it was made to spread out enemies in groups so you could target specific ones better. And, no one likes it.
This actually existed in Vanilla. I have to ask before making any claims on it, were you doing it in shapshifted form? That is because feral had an issue for many versions of WoW (at least until Cata and if I remember, even later) where your hitbox is too far forward for your melee hit to strike. This was proven in TBC where specials and white would hit at different distances.
Definitely a bug.
This was also in Vanilla. It has to do with how quest item looting worked back then. If there was an item you could not pick up on it and nothing else, that happened.
Not going to claim this is correct, but I seem to remember that when a mob aggro’ed its aggro range increased. Dont that that as cannon thugh.
Another Vanilla issue. It was annoying in many of the houses with mobs in them. If their or your hit box when through a wall even slightly, they would aggro players. Very annoying.
This was also a good one in Vanilla. Darkshore in Vanilla had a lot of these, usually with the mob in a tree. I was actually surprised to see it still in. There ARE ways to kill them, but the vast majority of the time, it just is not worth it.
This is one I am going to say I am not certain on. I seem to remember it being different for different abilities. Some worked fine, like thorns, others did not work at all.
The only time this should happen is if there is a special batched for the mob. I have noticed it happening more than it should as well.
This one is correct that it is a bug to my memory.
So yeah, some of those I know are not “bugs” in classic because they were in Vanilla, but others are definitely bugs.