Hi @TMJ,
This is expected behaviour, ArduSub includes a Pilot Input failsafe which by default disarms the vehicle if it hasn’t received a new control input within the last 3 seconds. It’s possible to disable the failsafe by setting FS_PILOT_INPUT to 0, but the recommended approach is to send regular control inputs just as you should be sending regular heartbeat messages. There’s an example here of periodic events, which may be useful 