Nighthawk c7800 dropping 5G

The past few weeks the C7800 has dropped the 5G channel repeatedly.  A power reboot restores the channel, but I can't seem to diagnose the cause.  Looked online and there is no firmware update for this model available.  Using several extenders with the system to reach detached above-garage living space, but those don't seem to be affected, still carry the 5G channel.  It's just the 5G channel coming out of the C7800.  Any suggestions?