Stun mastery bug

Hi, i want to report a potential bug where "Hits against you cannot be Critical Strikes if you have been stunned recently" doesnt work as intended

https://youtu.be/x9Ur-U4PGiw

I have Cast when stunned setup with penance brand, firestorm, bladefall, wave of conviction, purifying flame

As you can see from the video above, i didnt get stunned by the Apes that hit me. I am aware of cold crit hits cant stun you, so i equiped Eyes of the Greatwolf to convert all cold damage taken to fire, but it still didnt work. I also had Valyrium which make my stun threshold based on energy shield, and i had The Agnostic keystone to make my energy shield become 0 but none of them help me get stunned.

Then i decided to step on a cold bomb (for the first time) and get hit by it to get stunned, and yes i did get stunned once, and THIS should trigger the Stun Mastery which prevent Crit hit from the monsters, but i still didnt get stunned by the apes. Only after i stepped on another cold bomb (for the second time) and get stunned by it, those apes can finally stun me and trigger cast when stunned setup

After hundreds and close to thousand hours doing ultimatum (and inscribed ultimatum), i notice that the Apes type and Archer type monsters couldnt stun you properly. Is that a bug or am i missing something?

My pob is here in case anyone can spot a problem from it: https://pobb.in/BWw2gOfxHQjw