Was there a new credit card number issued after August 2018? You will have to re-connect credit cards when a new card number is issued. You should disconnect and reconnect your credit card. You can download into a csv file any missing transactions and upload them into the bank feed of your credit card.
Allow us to help you get your transactions synced to QuickBooks. However, we would need to get some information.
May we know the name of your bank? Have you tried clicking on the Update button to see if it downloads the bank transactions? If not, did you get any error messages?
Thanks in advance!