Good news for Apple Pay Suica users: word coming down Apple developer channels is that iOS 12.1 contains Apple Pay Suica fixes and performance improvements.
After updating to iOS 12 Apple Pay Suica users started complaining that Express Transit cards were sometimes unresponsive with Apple Pay demanding a Passcode/Face ID unlock at transit gates, or causing error flicker. It seems to be a performance issue across all Apple Pay Suica compatible devices: iPhone 7 (JP), iPhone 8, Revision B iPhone X, Apple Watch 2 (JP), Apple Watch 3 and the just released Apple Watch 4.
iPhone XS is free of the problem thanks to A12 Bionic bulletproofed Apple Pay Suica.
iPhone X Suica problem units will not see any improvement because it is a hardware issue for iPhone X units manufactured before April 2018. The only way to fix NFC problem iPhone X units is to get them exchanged. See the iPhone X Exchange Guide for details.
(Via Ata Distance)
Now I know when to upgrade unless work forces my hand sooner.