Look at which creatures are not being stunned. For some reason KI has made it so bosses (and i believe elite creatures) can not be stunned. Not much has been said on the subject so far :(
Just curious, did the problem where storm lord will not stun the enemy even though they have those stun shields on them ever been fixed
Those stun shields actually block the next four stun spells.
If you cast one Storm Lord, it will stun one round. But any other stun spell after that (including another storm lord, frost lord, or other stun spell) will be blocked the next four times. Only the fifth stun spell will work, after all four stun block shields have been used up.
The previous poster who suggested using Earthquake is correct. Using earthquake in between Storm Lords (or Frost Lords) will remove all the stun blocks and allow another stun spell to work.