If you enable the socket option "IPV6_V6ONLY" (see https://serverfault.com/a/408670) ipv4 and ipv6 can use the same ports on linux and the error is gone.
OK-Master
If you enable the socket option "IPV6_V6ONLY" (see https://serverfault.com/a/408670) ipv4 and ipv6 can use the same ports on linux and the error is gone.