I just noticed a path issue:
The second error (although it shouldn’t be the real problem here) the request
request: "GET /apps/theming/img/background/kamil-porembinski-clouds.jpg HTTP/1.1", host: "10.0.1.100"
should have been
request: "GET /apps-pkg/theming/img/background/kamil-porembinski-clouds.jpg HTTP/1.1", host: "10.0.1.100"