I'm having a similar problem. My Amex business account had two cardholders, and QB treated this as two separate accounts (this started when I set up the business five years ago). So even though Amex has multiple cardholders on a single account, QB always treated this as two separate bank accounts. Even though this is poor financial tracking, Intuit/QB support told me at the beginning that is how it is with Amex accounts. So I adapted and worked in this way for the past 5 years.

Now, since Jan 1, the behavior in QB changed. I first had to reauthenticate my Amex business account, and now it no longer recognizes the second card holder (only me, the primary). AND it does not import the second card holder transactions. That card holder does not have an AMEX account. So there is no additional login that i could provide to import those transactions.

This is a QB issue, even if Amex changed the way they send data, because this is how the data is imported and managed in QB. Please do not direct me to Amex, it is not an issue with Amex.