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

[ludiculous]

no I can be specific. The post you are linking says that with 100% wps, we can expect cadence to hit, then a wps attack, then another cadence. right here:

@TheMun

this means that with 100% chance to use a WPS, CS is triggered every 2 attacks.

so at 1:22. there is a AQC with cadence proc, then AQC, then whirling death (no cadence but I expect it to proc here), then single hit cadence proc. In this rotation there is both a wps with cadence proc, and a cadence without wps.