Ping is just used as a quick test to see if the network is routing packets properly. Although it's not always a good test if there's a possibility of an IP conflict and you're pinging the wrong device. How are the networks configured on the 2 gateways? Is there any VPN software that could be interfering with the communications where a network on the VPN is the same network as a local LAN?
If it's not on the same network subnet, make sure the firewall/router between the networks isn't blocking/filtering traffic on port 44818 from the gateway to the PLC.