It turned out that the empadronamiento was blocked because of the address difference between the utility bill and the lease. I implored them to look on Google Maps to verify the addresses were the same, but despite much sympathy from the staff, after a call over to another department it was determined that an in-person visit would be required to confirm the address. She also informed me that the address in the utility bill is probably the right one to use, even if the mailing address appears differently, because the physical location is the key data point.