I'm here to provide you some steps to get your online bank to download transactions again.
Try to log in to your QuickBooks Online company using your browser's private window.
Google Chrome: Ctrl + Shift + N
Mozilla Firefox: Ctrl + Shift + P
Internet Explorer: Ctrl + Shift + P
Safari: Command + Shift + N
Clear your browser's cache.
Use a different browser, if available, then see if it works for you.
Whenever you find yourself in this situation, you can always view this article for troubleshooting steps: What to do if bank transactions won’t download. It lists 3 separate steps, namely, manual download of bank transactions, check your bank's website, as well as fixes for specific error codes.
Let me know if you have any other questions by posting a comment below. I'll be sure to get back to you.