Hello there, @dan-gonzales.
QuickBooks Online is dependent on what and how AMEX shares the bank transactions with us. I recommend reaching out to your financial institution to know if they are changes made when downloading transactions.
Also, you can manually upload your transactions using the CSV file, make sure to exclude the transactions that aren't for the specific account to avoid duplication. This workaround is temporary until you'll be able to download the transactions automatically.
Feel free to check out this article for more details: Bank or credit card subaccount setup.
Categorizing your downloaded transactions can also keep your books accurate and can save more of your time while working your books.
Keep me posted for additional banking questions, @dan-gonzales. I'll be around to help.
