One of neat things about Apple Pay Suica is how easy it is to add, delete and migrate Suica cards to different iPhones. iCloud and Mobile Suica keep the Suica card information and balance safe and secure no matter what device it’s on.
There was one weakness however: the Suica card ID number changed every time the card was deleted and re-installed in Wallet. This was a problem for other apps that used the Suica card ID to soft link a service, such as JR Central smartEX. If the Suica card ID changed and the user forgot to manually update the new Suica ID number, the service stopped working. This is exactly what happened to me the first time I used smartEX.
This also applied to Suica Coin lockers which use the Suica card ID to lock and unlock. While it was highly unlikely anybody would delete and re-install an Apple Pay Suica card with their stuff locked away, the possibility was there.
Fortunately Apple and JR East have fixed this weakness. Now when you delete a Suica card from Wallet and re-install it the Suica ID number stays the same. JR East did not advertise the change but I suspect it was put in place the same time Touch and Go Shinkansen launched on April 1. Touch and Go soft links the Apple Pay Suica card ID number when you register.
With the new changes in place manually updating Apple Pay Suica ID numbers is a thing of the past.
UPDATE: the Suica ID number stays the same when deleting, reinstalling and migrating on iPhone but changes when transferring from iPhone to Apple Watch. I have not confirmed if Suica ID changes back to the original ID number or another new ID number when transferring Suica back to iPhone from Apple Watch.