Thanks for your help! Could solve this problem.
This is my solution:
xs set-env di-core JBP_CONFIG_JAVA_OPTS "[java_opts: \"-Dhttps.proxyHost=proxy.domain.de -Dhttps.proxyPort=8080 -Dhttp.nonProxyHosts="host"\"]"
Had to change the nonProxyHosts values. I set only the name of the server and removed all the other samples.
Now it doesn't crash and github works for me.