Ray might be onto something with the unit requiring internet access, I fixed my issue by connecting the unit directly to the router instead of through a switch.
I went back to look at my switches diagnostics as it’s a managed switch and noticed on the ports the sprinkler was connected to(i tried different ports, both have similar stats) it had a number of packet collisions, so i assume the switch was nuking the traffic to prevent further issues. for now though I’m happy enough to leave it plugged into the router directly.
Thanks for the help Ray, good luck Tom,