Phantom 5GHz signal from SaskTel Arris 5268AC gateway??

SaskTel installed an Arris 5268AC gateway as part of my infinet install. I am using it for both 2.4 and 5 GHz WiFi. I have noticed, using two different wifi scanners, that in addition to the intended and identified 5GHz RF channel there is a second channel on exactly the same frequency with no SSID. The phantom is always within 2-3 dB of the desired channel but almost never the same level so I am reasonable certain it is not coming from outside my environment. I have no other WiFi routers. The scanners show the MAC address of the phantom and it corresponds to Arris. If I unplug the gateway both 5GHz channels go away. If I disable the 5GHz radio in the settings, the desired 5GHz channel goes away but the phantom channel is still there!

Settings: 5GHz channel is set to auto and 80 MHz bandwidth. Primary network is enabled with SSID broadcast. I am using WPA2-PSK security with a custom encryption key. WPS is disabled and the 5GHz guest network disabled.

Just to confirm it is not guest network related I enabled the guest network and it showed up on the scans as a third 5GHz channel with a different MAC than either the primary or the phantom. I disabled guest after the test.

Does anyone have any idea what may cause the phantom and how to get rid of it??