Ray,
I use duckdns to access opensprinkler remotely. If DHCP assigns a new address then I have to change my port forwarding to make it match. A static IP would be better. Also based on my experiences with LibreElec my Time Warner furnished modem does not provide DNS at the gateway address (at least not reliably). At a minimum, it would be helpful to see what address opensprinkler is attempting to use for DNS. The ability to set a static IP, Gateway and DNS would be really helpful. Remoting in with SSH to do it would be fine.
Bill