I've experienced this, too, Mark.
Cache files are used to accelerate the loading processes of the websites or programs on your browser. Thus, remembering your old credentials and other common information you're using on the said browser.
We can do browser troubleshooting steps to get rid of any cache-related issues.
Let's try logging in to your QuickBooks Online account using a private since it doesn't store cache files. You can log in to a different supported browser, too. Each browser stores different sets of cache files.
Then, update your bank account sign-in information from there. If you can do it successfully, we can go back to your regular browser and clear the cache storage.
Otherwise, I'd recommend reaching out to our QuickBooks Customer Care Team. They'll be able to investigate this further and provide other troubleshooting steps.
Meanwhile, you might want to use a Webconnect file to import your bank transactions as an alternative for Online Banking. You can check out these articles for more information:
I'll be around if you need anything. I'd be glad to help.
