Don't forget that Arlo simply uses the phone's info to determine where you are. I'm not at all sure this is an Arlo problem. What device and OS? Have you tried a diferent device /computer?
Ive tried using an IPhone and iPad both with iOS 12.1 to enter my e911 address and both end up with the same error. Ive even tried entering an old address of mine in a different state and that worked, i.e. the old address showed up correctly after I input it into the e911 setup page. Ive also tried entering a random address from a few streets over but that ends up in another county too. I suspect there is some glitch associated with my home town in the software. I keep trying to enter my correct address in Suffolk county NY but after I hit save it records the correct street and house number but changes to the wrong county (Brooklyn NY). Makes no sense. I don’t understand the phone location connection and how that should affect where my home address is? Any ideas or suggestions?