As a principle, the local computer uses its "loopback device" with the 127.0.0.1 address.
Changing ports was the first thing I had checked. Since that didn't work for me, I thought that the 0.0.0.0 address indicated some other problem. 0.0.0.0 is really out of the ordinary. One could conclude that a procedure queried for an IP address, received nothing and continued without an exception (error).