Hello this was in the ptr offline as i was just lvling a character . Character was lvl 25 i have the Hawkmail Armor on Cannot be frozen. All other cold mobs that freeze do not freeze me so im sure its not the armor. When i went into the tomb to fight duriel the first few secs he had froze me i check to see if i was wearing the armor and i was just to make sure. Then i went to find a mob that freezes and did not get frozen.
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Cannot be Frozen does not work on Duriel.
This is not a bug and you posted in the wrong forum.
“Chilled” is different to “Frozen”. Not a bug. Game doesn’t make this clear.
“Chilled”, as it’s commonly referred to, is an Elemental Damage effect (Cold) that slows Character or enemies.
“Frozen” is a more powerful consequence of Cold Damage, which essentially paralyzes the target.
Keeno stated they were equipped with the Hawkmail Scale Armor, which has the Cannot be Frozen Affix.
The “bug” being reported is:
And you are correct. This is NOT a bug.
That’s because:
Duriel’s attacks can, not only “Chill” you but, “Freeze” you.
Source: Diablo Wiki - Cannot be Frozen
Notes
- This mod has no impact on the amount of damage taken from cold spells.
- The mod has no impact on the slows caused by Decrepify, Holy Freeze, Clay Golem and Slows Target.
- This mod is attainable through Sockets by wealthy players with a Cham rune.
- This mod has no effect against Duriel.
Drink more thaw potions 
Duriel is the only mob that even if you have cannot be frozen he will chill you. This is because he is a boss and was intended since game inception.