We also continue to have issues with American Express delegate connections.  

It is extremely helpful to create an individual log in for each card user rather than trying to import via the parent account - we have 50-60 cards at any time and USUALLY they sync.

Lately, Amex has been asking to verify our information - which they should not have to do for a daily bank feed!  I have one card that will not sync at all, it tells me that Amex has a question for me and I have to log in directly to answer their question, but when I log in directly everything is fine.

Amex & QBO definitely do not play well together, they need some relationship counselling!!