I found another "error" in the webconsole (Firefox and Chrome) for the Linux Version.
start
Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check https://xhr.spec.whatwg.org/.
init language
GET https://my.server.tld/gui/css/style.css 404 (Not Found)
checking browser
checking user terms
initing store and global
checking identity
initing main
onInit
GET https://my.server.tld/gui/version.json?1472712204748 404 (Not Found)
License FETCHED, Valid: true F.i {cid: "c5", attributes: Object, _changing: false, _previousAttributes: Object, changed: Object…}
app ready