The claims that are popping up that this has something to do with AppleCard are totally invalid, whether they're coming from Apple support, the AppleCard bank, or anybody else. If anybody "official" is giving you that answer then they're making up stuff cause they don't know, and, like most people, they can't bring themselves to say "I don't know."
My wife and I have been fighting this issue for several weeks (maybe months, I've lost track of time). We've only very recently (the last few of days) started using the AppleCard. Before that I was using my Costco Citi credit card for family purchases. Before that I was using a USAA credit card for family purchases. She has had the same "verification" requirement, as described in the original post, with each card that I've kept on file.
I don't have the answer. We've just now tried to change my wife's status to "Parent/Guardian" from "Adult." It asked for a verification again, but we'll see if it happens again next time she buys something (that shouldn't take too long).
In any case, can we please stop this false rumor that is has something to do with AppleCard right here and now?