Ah that is such a shame. I have the cash back card and the rewards are fantastic, but it's just frustrating how hit and miss it is to actually use it (most of the time Miss) although it's extra annoying when places take Amex, but not Amex Apple Pay!!!
From previous posts above I think it also plays up in Morrisons too for some reason.
AmEx acceptance is much wider than it used to be and they prominently advertised Apple Pay on their home page; just a shame it only works once in a blue moon...