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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.
@fanoush
you do have the MTU 53 line in the board file but I don't see matching linker setting like
https://github.com/espruino/Espruino/blob/master/boards/BANGLEJS.py#L43 however the 2c40 is the default so that's probably not it https://github.com/espruino/Espruino/blob/master/targetlibs/nrf5x_12/nrf5x_linkers/linker_nrf52_ble_espruino.ld#L7
when this is wrong softdevice fails at bluetooth initialization
but if the very same binary works in other device then it is strange, what about mass erasing before flashing?
and BTW if that D9 is BTN1 and you have bootloader too then the pullup can be set already by bootloader so main fw may not run