New faces I added in the iPhone Watch app showed up in My Faces but didn't reach my Apple Watch. Restarting both devices didn't help.
The iPhone's logs showed the watch-face library was stuck in an automatic "reset sync" (not the Reset Sync Data button). With 65 watch apps installed, the reset was too big, hit the limit of 1000 messages per 5 minutes and failed, so new faces queued up behind it. One face took almost three hours to reach the watch.
What worked for a while was removing the 7 watch apps with the most complications (I also pressed Reset Sync Data, so I'm not sure which did it). The reset dropped from 1946 to 927 messages and went through, and the stuck faces showed up the next time I added a face. About 90 minutes later a 939-message reset failed again, just over the limit counting the ~65 color-sync messages.
To see if you're affected, stream your iPhone in Console.app on a Mac, add a face, and search for "requesting reset sync".
I also filed FB25000090 because two queued Photos faces lost their photos when the reset went through. If you see it too, please file with sysdiagnoses from both devices (developer.apple.com/bug-reporting/profiles-and-logs) and mention FB25000073.
iPhone 18 Pro on iOS 27.2 beta (24B5089g), Apple Watch Ultra 3 on watchOS 27.2 beta (24S5091f). Same on the public 27.0 release.