Mobs lose label/health bars

When attacking some mobs they will initially show a label/health bar at the top of the screen. But there are times when mid fight the label/health bar will no longer show for one (or several) particular mobs from the enemy group.
Isn’t bad for trash mobs but on a boss or special fight its really annoying because you have no idea how much life they have left.

I’ve got issue with missing health bar on certains mobs. With some mobs there is no border around them and no healthbar (with a name of enemy) is showing up. Instead it showing health bar of my minion, but my mouse is on the mob/boss. Seems like my wolf mob border is “in front” of a enemy.

Here’s the link with a example:
My mouse is on enemy.