bluethoot low energy and bangle js2

you should not do the initialization of services inside NRF.restart(), that's meant for code that runs while bluetooth stack is completely disabled

https://www.espruino.com/Reference#l_NRF_restart

callback - [optional] A function to be called while the softdevice is uninitialised. Use with caution - accessing console/bluetooth will almost certainly result in a crash.

you managed to actually do both things advised not to do :-)