Charm of the Kusarigama does not 'proc' consistently

I made the (newly implemented) charm of the kusarigama to try out for some fun. At first, it seemed like the charm was not working at all as there was no change in damage, and while other charms had status buffs appearing, this one didn't seem to.

I took it for a spin in different realms and realised that the buff seems to proc "once in awhile" sometimes it would proc successfully 2-3 grapples in a row, sometimes it wouldn't for 10+ grapples.

Made a video with a few grapple attempts to show this. I was unfortunately not able to figure out any particular action that could consistently create a success or failure.

Was using Ornate Climbing Picks (with the charm attached) at the time and tested it in Abeyance, Welkin's Reach, Magwytch Marshes. All turned out the same.