Enough nonsense, if Apple can’t call it I’m calling it: iPhone X units manufactured before April 2018 have a NFC defect.
If your iPhone X was manufactured before April 2018 and you experience Apple Pay NFC performance problems of any kind regardless of credit cards, Suica, FeliCa or EMV, you should get your iPhone X replaced now while it is under warranty. Don’t wait. Check your manufacture date by pasting the serial number here.
There are more details, here and here, but the gist of it is that Apple did not iron out iPhone X NFC related production and QA issues until mid-April 2018, NFC issues that I believe affect all iPhone X users. I call good units Revision B iPhone X.
My iPhone X Suica problem unit made in January has problems with regular Apple Pay in America as well. Regardless of NFC protocol, Type-A or Type-F, performance is never robust. Half of the time the first read is a choke, the second read a clear. Most iPhone X users probably think a reader error is just a reader problem and miss it. It’s an iPhone X NFC problem.
Put it this way: with an iPhone X made before April 2018 the second read is always successful, with a Revision B iPhone X the first read is always successful. Which one do you want?
If you want robust, reliable NFC on your iPhone X, Tim Cook’s Apple is not going to make it easy for you. You have to check your iPhone X manufacture date and get a Revision B iPhone X replacement from Apple. An exchange guide for that is here.