Can anyone explain why cadence at 100% wps sometime hits every 2 and sometimes every 3 attacks?

I’m quite confused

why is cadence not happening every 2 hits? (I am seeing sometimes it needs an extra hit even with 100% wps).

There is 100+% wps in the video. See the 4 nightblade WPS skills (88%) and the bladesworn Talisman (15% chance), total 103%.