AP Bank Account not showing up in list though already applied to two sites

We have a bank account that will not populate the List of Values to select for a Supplier or its Site even though it is already assigned to two of the Supplier's Sites. The two previous sites are Electronic/ACH sites, but when selected will not populate the bank account information on the AP invoices, so we set up the new site to see if it works, but we cannot assign the existing bank account. Please help with these issues. Is there a way to setup the bank account again even though it would look like a duplicate? We need to