This almost sounds like there is more than one device attached to the ONT side of the network (i.e. two routers with WAN interfaces). The 4-6 hours is suspicious because that would. be the typical DHCP renewal window for the WAN side of the connection. So ... the router DHCP's an address, gets bound via MAC to theONT as the authorized device, but when the lease renews or expires, something else steps in and snags the address/mac assignment.
When this lockup occurs -- right after it occurs -- if you power off the Netgear and start up again (just the Netgear, nothing else), dods service come back or is it locked out for say another 4-6 hours or until you power cycle the ONT or something else?
With that said ... I kept having problems with my Nighthawk router where the WiFi would go offline until I power cycled (or certain devices refused to "see" it). There seemed to be some kind of firmware bug -- the router itself still worked -- direct connections and the 5ghz band were fine -- just the 2.4ghz band went out to lunch. Think it may have hand something to do with the bandwidth steering it was doing trying to choose between 5ghz and 2.4ghz and incorrectly trying to force 2.4ghz only devices over to 5ghz and blocking them from rejoining the 2.4ghz network -- I eventually replaced it with a TP-Link C5 Archer and have at times also used an ASUS (don't remember the model), and both worked flawlessly -- neither of which coincidently have bandwidth steering or "SON" as Verizon routers call it capability.