Nighthawk M5 frequently stops working

We use our Netgear Nighthawk M5 on a location where there is no wired internet available. The M5 is connected to the power adaptor 24/7. It is used in combination with an internet only simcard for wirelessly accessing the internet and connecting our security camera recorder via a utp cable to the internet making it possible to check in on the security system when we are elsewhere. After working fine for more than a year now it frequently stops working: Wifi is not available and it is also not possible to access the security recorder remotely. When at the location pressing the button of the M5 solves both problems. It looks as if the device enters a sort of sleep mode. The problem can last several days and then suddenly the M5 starts working again making it also possible to access the recorder remotely.