Let's isolate what causes the transactions to not sync, allaboutthefaces.
There are several possible reasons why transactions won’t download. They include:
A connection issue between your bank and QBO.
The financial institution’s server is offline.
Error messages or codes that require you to perform a certain task.
In the meantime, let's manually update the connection by clicking Update on the Banking page.
If the download seems stuck, you may want to log in to your bank account and check for any page maintenance.
If you have more than 90 days of transactions to download, you can manually upload them into your QuickBooks Online account.
I'd also like to confirm the name of the online bank account you're having issues with. This is so I can provide specific troubleshooting steps to resolve the issue at hand.