only "Cannot be stun", but also cannot be freeze

I found that I cannot freeze the monsters that has status "cannot be stun"(there is not cannot be freeze). And yes I am sure I was hitting criticals (with the obvious sound effect) and yes I do enough cold damage to freeze them, tested on same level other elites that without "cannot be stun" I can always freeze them every couple hits. It just doesn't seems to work on "cannot be stun" monsters. I talked to a MOD in game, and he want me to file it here. Please check, thank you!!