Your browsing history can be the reason why you're unable to connect your bank account. Let's perform some browser troubleshooting steps to connect and update it successfully.
Let's start by accessing your account via incognito or private window of your browser. To check if this unexpected behavior is related to your current browser or not. To do so:
If you can connect it without any issues, you can clear your regular browser's cache so your browsing history can start from scratch. However, if you receive the same result, let's access your account and connect your bank account using other browser apps.
Lastly, I've also included this helpful article in case you'll want to categorise or match your downloaded transactions: Categorise and match online bank transactions in QuickBooks Online.
Keep me posted in the comments if you need more help. Hope to hear from you soon.