Haven't done solid testing on it but have randomly used it a bit... I'd say around 10%ish but not a big sample size so hard to tell. Also haven't tested if it stacks with others... would be intersting with the new occasionally absorbs dmg one and another absorb magic or physical and gear for that lol
I know the old "Occasionally Absorbs magic damage" had an absolute ***proc rate. Wore it through a Glavoid, 3 Sednas, and a Durinn and the first time it procced was when I was trying to homepoint via an Ephemeral.