Crushing Ruin's CC "Immunity" Not Working

Comparing to Catastrophic Pummeling as an example, Crushing Ruin's crowd control immunity does not appear to function against enemy holds and stuns. I have tested against various enemies (Ape, Gravitar, Baron, Black Fang, various mobs (Trey Kings, Sovereign Sons, Dogz, Horrors, Elder Worms) and have yet to have the ultimate not get canceled by a hold or stun from an enemy during any part of the maintain.

Since Catastrophic Pummeling does not seem to have this issue, I would suggest reviewing to see if the CC immunity is working at all.