Device keeps resetting

I correctly setup my Extender and use it for often several weeks., Then for no apparent reason I notice that all the complete row of LEDS are flashing.  My manual says that device is trying to do a factory reset but that never happens it will flash for days.  Eventually I end up going through pressing the device reset and then setting up as new device etc.  This works but several times although my router wifi passwords are correct (other devices are correctly connected) it says unable to connect incorrect roter password.  I presevere and eventually it connects.  I then wait till the next time it fails. If it wasnt such an expensive device I would tech it to fly off a tall building.  Netgear are no help as I am 10 days past the years warranty!  Firmware is latest.