I finally got back to Japan and called Apple Support. 30 minutes later I had an exchange iPhone X on the way to my apartment via Yamato-bin that arrived the next morning.
The first order of business was checking the serial number and manufacture date:
A 2018 Week 30 production unit, so far so good. After restoring Apple Pay Suica to the Rev-B iPhone X, I took it for a spin along all the well-known trouble gates of my JR route: Asagaya, Koenji, Ikebukuro and Shinjuku. The ride was finally smooth and error free as iPhone X should have been all along since day 1.
The feel of Apple Pay Suica on a Rev-B iPhone X matches what readers have been reporting: NFC performance is snappy with none of the problem iPhone X lag or errors going through the transit gate. The difference will be noticeable if you are familiar with Apple Pay Suica performance on iPhone 7.
If you are a Suica commuter road warrior with a iPhone X Suica problem device, you should get an exchange for a Rev-B iPhone X. It’s boringly reliable. You deserve nothing less.