You can sign in to QuickBooks Online and then copy the link to your bank's website by clicking the Pencil icon on the blue tile, then select Edit sign in info. From the window, click on the link, so you be routed to the official login page of the bank.
Also, it's possible that cookies made this unexpected behavior in QBO. You'll need to isolate this using a private browser to see if the same thing happens.
This browser mode helps you free from cookies that make QBO unable to load the same page, like Banking.
Make sure to open a supported browser, then follow the shortcut: