If your system goes into hold you must be using PCM receiver and you have a serious problem. Get and install a PPM receiver for testing purposes. Do a range check with and without the engine running. If you don't have a problem with the PPM receiver installed your PCM receiver is bad.If you don't have a problem with the engine not running and do with the engine running disconnect each servo, one at a time. If the problem goes away when one of the servos is disconnected clean the connections to that servo and try again. If you still have a problem replace the servo. Try replacing the battery and switch.
Check and clean all of the connections of the ignition system especially the spark plug lead. If you still have a problem replace the ignition battery and its switch.
If you have done all of this and you still have a problem find another place to fly.