Remove all occurences of "--ping" but one. It's unnecessary to provide this option more than once anyway.
I guess you specified the --ping option in the client config and additionally the server is pushing this option to the client. The --keep-alive option also includes --ping (see
https://community.openvpn.net/openvpn/wiki/Openvpn23ManPage). So if you specified --keep-alive on the server OR on the client then you should remove all instances of --ping.