No, that's definitely not it. There is no set rotation through SFO, and the flights mirror plenty of other flight patterns which aren't being cancelled. For example, CX879/870 has an identical plane type and pattern as CX837/838 (YVR). CX851/892 has similar with CX890/899 (EWR). Neither of the others face cancellation.

What's happening is very similar to LAX after AA launched. Prior to AA, CX had 4x dailies to LAX and oened the market.

​​​​Once AA launched, CX periodically cancelled CX898/897 and sometimes CX884/885 too. Eventually CX fully cancelled CX897/898. HX has since entered the market; so LAX is now served by up to 5x daily flights. And CX still occasionally cancels CX884/885 in th low season.

At SFO, CX themselves added capacity by making 892/852 daily, and HX also launched. Plus you have SQ and UA flying daily. So SFO now has up to SIX dailies to HKG on the days HX runs. My guess is capacity is....overserved at this point.

So my bet is loads or yields are weak and that's why CX is cancelling one off days.