Let's get your online bank account working in QuickBooks Online (QBO).
The first thing I'd like to know is the specific bank account that you have. It's an important piece of information since it will allow me to provide you specific troubleshooting steps to resolve the issue you have.
At this time, what I suggest is for you to open your browser's private window. This isolates cache, which is the common culprit of unusual behaviour in browsers.
Google Chrome: Ctrl + Shift + N
Microsoft Edge: Ctrl + Shift + P
Firefox: Ctrl + Shift + P
Safari: Command + Shift + N
If that works for you, go back to your regular browser and clear its cache. Otherwise, open a different browser that's available for you.
Whenever you encounter any issue with your online bank's connection and you need to have your bank balance updated, see this article: Manually upload transactions into QuickBooks Online. It's a step by step guide on how you can get your transactions from your bank's website and upload it to QBO.
Tag me in the comments below if you have other questions, and I'll get back to you.