Why is the Ai to all units so incredibly bad?

About half the rounds one or two units will just spaz out and stand there doing nothing, no stuns, banish or other effects** with a lovely massive space to move to to attack other units**. Usually after an enemy unit dies where they spend about 3-5 seconds turned facing a random direction and doing absolutely nothing before finally snapping to another unit which is already too late. This happens to both Ranged and Melee.

(This bit for those that cannot read) I repeat no other effects were on these units, no stuns, silences, ice etc.