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.
Apple Pay Suica users report the following performance issues after updating to iOS 12.0 and watchOS 5.0:
- Transit gate error flicker
- Unresponsive Express Transit at transit gates with Face ID/Touch ID/Passcode Apple Pay authentication request
- Suica card balance doesn’t update
- Slow or failed Apple Pay Suica Recharge attempts
Affected devices: iPhone 7/7 Plus (JP models only), iPhone 8/8 Plus, iPhone X, Apple Watch Series 2 (JP Model only), Apple Watch Series 3, Apple Watch Series 4.
iPhone XS is not affected by iOS 12 Apple Pay Suica issues thanks to A12 Bionic.
Fortunately iOS 12.1 has Suica bug fixes: Apple Engineering closed my original iOS 11.2.5 Suica error bug report filed in January 2018 saying the issue has been fixed in iOS 12.1.
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.