OpenVPN client inactivity errors

I have configured up my Netgear R6220 as an OpenVPN client. It connects to the server fine, firewall set fine, and all traffic routed as expected.
Internet connectivity works as expected (location as per the server location). I can also access all services in the remote network as expected. ping and ping-restart are set as 10 and 120.
I can SSH to the "gateway" (server VPN subnet IP and local subnet in server locaton) ping it etc. but still I get "Inactivity timeout (--ping-restart)" occurring in the client logs (and the VPN re-starting)
Server logs report a re-connect from the client, and a warning about multiple clients with same connection credentials.
I have other devices connecting from the same network, similar client configurations (only difference is client cert) and they show no similar behavior. What am I missing here? this makes no logical sense to me.