This must be a bug on apple's part. I have my developer devices (iPhone 16.0 (20A362), Watch 9.1 (20S5055e)) totally out of sync and my personal devices (iPhone 16.0 (20A362), Watch 9.0 (20R364)) working perfectly. Both are running the exact same version of my app (thru TestFlight). Dunno if it's the developer iCloud account or the beta software on the watch.

From what I learned the past year there is no way.

Honestly have to say I don’t know how exactly I fixed this. My hunch: don’t overstress the background app refresh budget or watchOS gives your app the cold shoulder. :-/

From my analysis this is an issue in watchOS 9.1 Beta. I now have two "debug" Apple Watches paired to my "debug" iPhone. One iCloud account all across of course. Sync from iPhone to Apple Watch with public watchOS 9.0 works flawlessly, with watchOS 9.1 beta: no dice.