Could this be a serial number mismatch, e.g. the serial number on the box came from another unit? Is there a legible number on the back of the unit itself? Does it match the barcode?
Are any incoming connections to the device possible (web, telnet, SSH)? If so, that might be a way to verify the serial and possibly get details about an error.
Based on @hfiennes 's comment, I would assume that the connection attempts should have logged something on the Rachio cloud, at least an error message. I hope that someone at Rachio can search their server logs for the MAC or S/N and tell you what they see.
Based on
you may be out of luck, though apparently if it can’t connect to Wi-Fi for an hour, it goes back to awaiting blinkup and might reset other stuff.