FYI - To all involved here.

I just got off the phone with AMEX, and they are aware of this issue and are working on it.

So glad I didn't cave and pay the $120 for upgraded customer service for QB to tell me that there's nothing they can do, and that it's a problem with AMEX. Feels like this should have been something that QB could have told us right away?

Lesson learned, go directly to the financial institute first, and save myself 24 hours of headache on this forum.