I also had some issues with the iphone x, although I managed to eventually enroll it (according to the Aunty). I think it's a combination of the cheap nfc pad they are using and iphone x's weird nfc placement for me at least. I've had some issues paying for stuff at a particular toast box using my iPhone x.
Luckily I registered my apple watch too, which I'll be using mainly anyway.
Where's the NFC chip situated at on the iPhone X huh?