If you set the IP address in the Gateway configuration, as you did, I suggest you to enable the IP filter in the system settings. Because, as I mentioned before, IP address configuration for logs in the gateway are mandatory only if you enable the IP filter.
Then, if logs are empty, causes could be:
1. Gateway didn't send logs;
2. port 1514 is closed in the customer firewall so, HSNM, can't receive logs;
3. Syslog service, for some reasons, was stopped. But it is quite unlikely;
4. IP filter has been enabled in the system settings but in the gateway configuration the IP address where the logs come from hasn't been set. Or a wrong IP address has been set.