thank you for your help and patience !..
unfortunately adding node_modules :
ignore: ['build/**/*.*', 'static/**/*.*', 'node_modules'],
seems not to change anything my side.
I tried to reinstall everything from scratch, too, with no avail. Do you know if there is some sort of cache somewhere for npm, and for safe related stuff ?
I really do not understand how it may not work when I delete the whole folder and git clone again.