I found my error.
The error came from the fact that I tried to install npm modules into a synched folder from the guest machine.
What I did:
1 - vagrant up
2 - clone your moodle mobile into a folder ignored by vagrant. I used "~/mm"
3 - install all your npm modules there. https://docs.moodle.org/dev/Setting_up_your_development_environment_for_Moodle_Mobile_2
4 - copy your node_modules folder from ~/mm/node_module to your vagrant dir
That worked for me
Hope it helps