You could try just adding a handler here and see what happens? https://github.com/espruino/Espruino/blob/5be68a80baeca1ab4e6ab31b9d78244afd2092c1/targets/nrf5x/bluetooth.c#L1445
Even if you only printed to the console you might be able to see if it is at least getting called?
@Gordon 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.
You could try just adding a handler here and see what happens? https://github.com/espruino/Espruino/blob/5be68a80baeca1ab4e6ab31b9d78244afd2092c1/targets/nrf5x/bluetooth.c#L1445
Even if you only printed to the console you might be able to see if it is at least getting called?