There are a couple of ways to address what you need. First, you can set up IFTTT notification on your remote controller, so that every time a station finishes running you receive a notification. This will make sure the remote controller is receiving command as expected.
Second, if you don’t mind changing the firmware code (which on OSPi is really easy, just involves running built.sh to recompile the firmware), you should look at this line:
https://github.com/OpenSprinkler/OpenSprinkler-Firmware/blob/master/OpenSprinkler.cpp#L1126
in OpenSprinkler.cpp. If the timeout has reached, or the client has lost connection, that means it’s not able to reach the remote controller, and you can add code around here to log this event, or send a notification.