Obviously something happened, you have checked the equipment and found nothing; that leaves intermittent equipment failure or RF interference or it could be there is nothing wrong with the equipment and the RX lost sync with the transmitted signal for no repeatable reason.
While many hail spread-spectrum as the holy graile, the fact is no RF transmission is bullet proof.
These things are very hard to troubleshoot in person much less on an internet forum.
Unplug everything and then plug it back in, replace the switch in the plane, on the TX if the antenna is connected to a board with a screw, loosen it and then retighten it, look at the solder connections .... once you check everything and do a 10 - 20 minute range check the only thing left to do is to send it back or fly the plane again.