Nighthawk AC4000 3x3 tri band WiFi Router—going off and on with ATT fiber Giga, mainly Apple devices

[Jmvlg]

Hi, my router has 4 years and since some time already, the internet goes off and disappears from the WiFi list of available networks on Apple. I reset quite often the fiber, modem, router boxes. Problem remains. ATT has this security free service (firewall?!?!) turned ON, could it be the problem? Should I switch it OFF? I believe I had donde that too and no big difference on R8000P going OFF and ON, irresponsiveness. Thank you

[FURRYe38]

What Firmware version is currently loaded?
What is the Mfr and model# of the Internet Service Providers modem/ONT the NG router is connected too?
Be sure your using a good quality LAN cable between the modem and router. CAT6 is recommended. 

What channel configurations are currently set on the router?  Try 1 and 40.

Be sure to disable any MAC Address randomizers on phones and pads while at home:
https://community.netgear.com/t5/Nighthawk-App/NETGEAR-Mobile-Applications-and-Apple-Devices-FAQ/td-...