Netgear R6400 - WiFi 5GHz channel disappear regularly

Symptom:

5GHz channel disappear after few days 

Solution:

change the wireless channel to another less interface with nearby AP.

Reference:

https://kb.netgear.com/25182/Resolving-poor-5GHz-wireless-range-signal-from-my-NETGEAR-router

https://kb.netgear.com/25057/NETGEAR-Range-Extender-is-not-detecting-the-5GHz-wireless-band-of-the-NETGEAR-router-or-the-5GHz-connection-is-intermittent

Netgear R6400 - WiFi 5GHz channel disappear regularly