Your first post is what I was referring too - the USAA issued Amex cards will not work at the USAA rollout, only the Visa and MC branded cards. I quoted the part in the link I posted that said it. I personally don't have an Amex card of any flavor any longer. They did NOT do right by me, and I choose to no longer do business with them. Oddly, one of my Supervisors had a similar occurrence and ceased using them too. It was nice to find someone else that "got it". I don't begrudge anyone that has great experiences with them - and in their defense, they thought they were doing me a favor. I looked at it differently.
The key is, the issuing BANK needs to support Apple Pay before it will work - it doesn't matter which label the card has, Visa, MC, Amex because it needs to be in place by the bank first.