CAUSE 1: Configuration issue
CAUSE 2: SELinux is blocking
CAUSE 3: Syslog-ng is not starting correctly and getting error.
When the IP is missing from the source definition, then syslog-ng will listen on all interfaces. When there is any IP address, then the source will use that IP address found on the server.
Set SELinux to permissive or disable it. For more information on how to configure Selinux see the following link: Using syslog-ng with SELinux in enforcing mode
If it continues to fail, please see the troubleshooting section below.