This is on Ubuntu 18.04, right?
The problem is that it’s using an old version of npm (3.5.2) which has issues with peer dependencies, the functionality I had to add to get the Roon API working again.
What I did on my Kubuntu install is downloading a more recent version of node/npm and using that instead of the provided version. It might be necessary to update the path variable in the service file, depending on the installation location. If necessary I can provide more details.