I appreciate you doing the troubleshooting steps, @Gonzosgone.
Since the issue persists even after doing the troubleshooting steps, I recommend contacting our Customer Care Support. You can work with one of our specialists in creating a ticket letting our engineering team investigate the root cause of the problem raised saying you haven't been able to connect your QuickBooks Online account to the Santander Bank account.
Here's more information about downloading the transactions from the bank. Then, upload the file to your account: Manually upload transactions into QuickBooks Online.
Feel free to post here on the QuickBooks Support page again if you need anything else with QuickBooks banking. I'll be right here to help you anytime. Have a great day!
Hello Community users, we just wanted to pop in and update this thread. The senior banking engineers at QuickBooks resolved the issue with the banking updating on the 23rd of January and the investigation was therefore closed. If you have any similar problems with the banking updating, please let us know and we'll make sure to look into that straight away for you.