Several times this evening the 5G SSID disappeared from mobile devices while the 2.4 SSID remains on our Hitron CGNM-2250 - SHW. 

I restarted the router each time and that seems to have remedied the issue until it returns about an hour later. Has there been a firmware update recently for the router? My router's hardware version is 1A, software version is 4.5.11.9.1.