The workaround kind of did the trick. I can now deploy my project again, but the 3D Model i linked to the 3D Widget in my GUI is not displayed anymore. The 3D widget is dark and in the upper right corner is a loading icon. In Motorcortex.io it works fine. Could this still be related to the original issue?
On another note: When i access the controller via its IP Adress 192.168.2.100/list there are many old gui files that i would like to get rid of. How can i access these files on the controller to do some "spring cleaning"?