I had the same issue on a different nrf52840 board http://forum.espruino.com/conversations/354468/ not sure if this would help but this sounds like what I experienced before
@parasquid started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
I had the same issue on a different nrf52840 board http://forum.espruino.com/conversations/354468/ not sure if this would help but this sounds like what I experienced before