Let me help you in importing your bank transactions.
Are you manually uploading the bank entries? If so, make sure that the file is in the correct format and you map the data properly. I recommend using a CSV file. Check this link to see common errors and how to fix them: Fix bank upload errors in QuickBooks Online.
For online linked accounts, we need to check if the bank has system issues cause that can result in connection problems and the transactions not to download.
We can also manually update it which helps to bring in the bank transactions. Follow these steps: