For what it's worth,
I tried to look and see if the app mentioned NFC and it they don't from what I could glean of the ones I looked at. Google Pay and Samsung Pay apps both mention control Near Field Communication, however, unless I'm looking in the wrong place on my device, NFC access doesn't seem to be a Google permission even though I found it under permissions for both those apps on their app pages.
The two things that are bothering me are;
King Mustard didn't believe that he had set up Samsung Pay on the previous device and the fact that it works on this device, although only when the banking app is open. Setting up Samsung Pay isn't something that you simply forget doing. It's also not something that is so easy to do that it could be done by accident. You also have to unlock Samsung Pay to use it, so there's no way, with the screen off you're making payments. Add that nothing is set-up on this current device and it works, if you have the app open. IDK but to me that says the app is responsible for the transfer of information over NFC and the device is controlling how, when and where. I think B. Diddy is on to something with Huawei and either how they handle background apps or NFC.
King, I would check your NFC settings to see if there was a way to have NFC on all of the time or when the screen was awake. I mean it wouldn't be too much trouble if all you had to do was wake the screen. It could be a permission on Huawei, I don't know if MFGs can make things outside of the Google list of permissions permissions, but I don't think even as a permission it would make much difference how it's managed or controlled in this case because you just want it on when the screen is off. It might be worth a look. If for no other reason S&G.
Personally, and this is just my opinion, I wouldn't want it to work as you described it working on your old S9. If the screen can be asleep and simply holding it up to a reader was enough to make payment, without any input on the users part, that sounds risky to me. I stopped carrying my new Capital One card out of fear of skimmers and if it is working all the time your phone could be just as susceptible.