The arrow is shown when the controller pings the router to see if it’s still connected. It does so every 30 to 60 seconds (forgot the exact interval). If the screen gets stuck with the arrow, it means the controller is not able to reach the router, so typically indicating a connection problem.
Are you using DHCP or static IP? If you are using static IP on OpenSprinkler, you have to make sure to set the correct gateway (i.e. router) IP. Otherwise the controller will not be able to reach the router.