ember electron:package build failed, caused by ember-browserify

when I want to build my ember electron app with ember electron:package I always get the error: Build failed.

File: assets/vendor.js (91129:6)

    The Broccoli Plugin: [UglifyWriter] failed with:

followed by several lines of "Error at...:" (always within node_modules)

I could figure out that it must have something to do with ember-browserify. I am importing this node module in a service.js file:

import Usabilla from 'npm:usabilla-api';

The curious thing is, that with ember electron (like ember serve) everything is fine and I can use the node module without any errors. Issues only occur when I want to package the app to the .dmg and exe files for distribution.

What am I missing ? Thanks for any help or hints!