The synchronization of bank transactions in QuickBooks Online (QBO) depends on your bank. Therefore, contacting your financial institution first is recommended to confirm if the transactions are posted on their end.
Since it's good on their end, can you please share your bank's name for me to check here on our end if there is an ongoing issue with downloading transactions from them to QBO?
Nonetheless, we can try manually downloading the latest transactions available to sort this out. Here's how:
Go to the Transactions menu, then select Bank transactions.