There seems to be a problem with Apple Wallet for some Apple device users. iMore says some users running last week’s public releases of iOS 15.3 and watchOS 8.4 are falling out of sync. According to the report:
A number of people are experiencing sync issues for cards added to their iPhones — they aren't always appearing on their Apple Watch after updating to the latest versions of iOS and watchOS.
The issue isn’t big in terms of number of people affected, though for people affected, it’s a big enough thing to complain about. The piece points to one such complaint on Reddit, with that person saying:
iPhone 12 and Apple Watch Series 3. No coupons/membership cards added on the iPhone have successfully been synced to the Apple Watch since I updated to 8.4 and 15.3. Interestingly enough, removing a card from the iPhone does not seem to sync to the Watch either, but removing a card that exists on both devices on the Watch successfully syncs to the iPhone.
With so many variables, it’s hard to say which element is gumming up the works. Apple is said to be looking into the issue. So far, it has not offered a timeframe for a fix.