QB launched an update that ended up mixing some fields up in their database and caused your customer ID for your bank feed login to be changed by a regex that formatted your bank login ID as if it was SS# or EIN and also changed EIN to be a 4-digit chart of accounts reference number or something similar. In essence, you will need to contact quickbooks support, explain the issue, and submit your company file for data repair services as QB desktop will not allow you to change your customer ID due to the EIN and Customer ID being the wrong format, giving an error when trying to save, and not allowing you to actually save any changes.
There's a support guide that explains that you can change or deactivate your bank feeds by exporting your chart of accounts as an IIF file, modifying the relevant lines, and importing the updated IIF file but this still errors due to the above reasons. Basically, someone at Intuit made a mistake, pushed an update that caused this issue, and either hasn't realized the issue yet, or the issue can't be fixed by pushing a new update due to the fact that it changed your existing ID and EIN / SS# for those fields and they can't simply reverse it with an update.
I've not tried this but it's possible you could revert to a back up prior to when you started to experience this issue and that might fix the problem but you'll have to re-enter all the data since that time such as bills, invoices, etc. I've contacted support about this and am waiting for a response from the data recovery team to help fix the file for me.
