Can you try running:
lsof | grep usbmodem
and see if that returns anything? It's possible it'll show something using the port...
The suggestions here may help as well. They are for Arduino, but could apply similarly to Espruino
@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.
Can you try running:
and see if that returns anything? It's possible it'll show something using the port...
The suggestions here may help as well. They are for Arduino, but could apply similarly to Espruino