Do you notice any flashing lights on the ESC while it's not working?

The first thing I would do is make sure the software is updated and all the settings are reasonable (such as low voltage cutoff, timing, etc.). Then I'd check all the solder joints, especially the bullet connectors on the ESC since castle doesn't always get a solid joint... I've seen it more than once.

Next thing to try would be a capacitor. If the BEC voltage gets too low it can cause the receiver to reboot. Generally you'll lose steering control when this happens but maybe there's some fluke with your particular setup where the throttle stays off for a few seconds.

Beyond that I'd tend to blame batteries or radio but it really could be anything from a bad ESC to a motor... Hopefully one of those first two simple things takes care of it. Good luck!

-Eric