There aren't any limits on how many banks you can link in QuickBooks Online. Let's determine the proper action to take so you can successfully connect another bank account. Can you share the name of your financial institution so I can check for possible issues with the bank?
The most possible reason that it's still downloading is that your bank may have ongoing system maintenance. You can log in to your bank's website to verify the information and check for any alerts that may need your attention.
In the meantime, you can also access your account using an incognito window. This mode eliminates the possibility of a cache issue on your browser since this doesn't save any site data that sometimes cause unexpected behavior in the system.