Thomas, thanks for this hint!
I could set all the values, restaged and restarted the app, but when I build the app there is no difference. 
The variables are looking fine.
But the error messages is still the same.
npm http request GET https://dummy:51007/squel
npm http 404 https://dummy:51007/squel
npm ERR! Linux 3.0.101-71-default
npm ERR! argv "/dummy/usr_sap/CH2/xs/ea_data/dummy/executionroot/30579e17-48ff-49ae-bce2-da5f0ba05b83/app/resources/nodejs/vendor/node4.4/bin/node_main/node" "/dummy/usr_sap/xxx/xs/ea_data/dummy/executionroot/30579e17-48ff-49ae-bce2-da5f0ba05b83/app/resources/nodejs/vendor/node4.4/lib/node_modules/npm/bin/npm-cli.js" "install" "--registry" "https://dummy:51007" "-d"
npm ERR! node v4.4.0
npm ERR! npm v2.14.20
npm ERR! code E404
npm ERR! 404 no such package available : squel
npm ERR! 404
npm ERR! 404 'squel' is not in the npm registry.
npm ERR! 404 You should bug the author to publish it (or use the name yourself!)
npm ERR! 404 It was specified as a dependency of 'tinyjs'
npm ERR! 404
npm ERR! 404 Note that you can also install from a
npm ERR! 404 tarball, folder, http url, or git url.
npm ERR! Please include the following file with any support request:
npm ERR! /HANA/usr_sap/CH2/xs/ea_data/dummy/executionroot/30579e17-48ff-49ae-bce2-da5f0ba05b83/app/tomcat/temp/builder/sap.nodejs/builds/build-767109958341041024/tinyjs/npm-debug.log
Any ideas?