Saying it's only compatible with a few specific proprietary devices isn't stated anywhere in the advertising, let along when the sales people are trying to talk you into buying the service on the phone, neither is the anti-root stance being taken.
Overall very disappointing so far and not a good attempt at retaining TV customers in it's current form.
Actually it is...
Try connecting your Android TV box to the router directly, using a CAT-5e ethernet cable, if that is possible. The hard-wired step completely bypasses the issue of the WiFi SSID changing from band to band, and also avoids using any potentially incompatible WiFi adapter formats, such as the older ABG vs newest AC Wave2.
I think you're going to find that the issue is in your router or ATV disallowing the connection, not in the Spectrum app itself. I see at least two possibilities there:
1) Your Android TV box's OS may not support roaming between WiFi bands without establishing a new connection, AND
2) You may have created invalid SSIDs for your WiFi device. Starting from your chosen WiFi as the basic name, the industry default SSID naming convention would be WiFi on 2.4 GHz and WiFi-5G on the 5 Ghz channels.
The device-specific version of Android OS embedded in your unit may require that you comply with the expected naming conventions.