Bad Gateway 502

Did everything as it is described in the readme (for HTTP at 127.0.0.1), all containers are running fine, but I get a 502 as soon as I load the host-url via browser.

There are a few issues mentioned in the web like https://stackoverflow.com/questions/47429540/nginx-502-bad-gateway-within-docker-stack but none of the suggestions helped so far.

Any idea to solve that issue?

Best regards