Hello!
A new modem update was released to address concerns about accessing certain websites and gaming online. Several months ago we suggested disabling UPnP in the modem to address this, but this is no longer needed thanks to the update.
This update also addresses the disappearing 5 GHz WiFi network concerns you've reported, so this should no longer be happening.
If you still have concerns despite the update, let us know by starting your own thread in the Tech Support board to provide details about your experience so we can better assist you.