Cannot target mobs with basic mele attack

Sometimes targeting mobs for basic mele strike is impossible. I click on the enemy and nothing happens.
It does not happen often - once or twice per map but still can be deadly - need to dodge, drink potion and pray not to die before I can start eliminating the mobs. It is 50/50 in terms of surviving this - pretty annoying and frustrating.

I tested on lower levels more when it happened, and I know it is not due to stun or any other CC - clicking does on the mob simply does nothing - not even moves my character and I use click to move.

Maybe I'm too close to mob or something else is going on.
Please take a look at this.
I know that most ppl runs through map with AOE screen kills but basic fun stuff should still work :)