bekesizl: Compiling the OpenSprinkler isn’t to complicated. You have to follow the instructions given in the OpenSprinkler Support section. Some hints are also given in the forum thread: Error building firmware from source.
If you change the CHECK_WEATHER_TIMEOUT parameter in main.cpp to 1 hour as described above there is a good chance that you see the “Empty Response” answer only once or twice per day. In this way you can probably use your own local weather service for the OpenSprinkler Water% calculation.
I’m not sure what causes the issue. I’s maybe some timing problem due to the longer data travel time if WiFi repeaters are in use. Maybe the OpenSprinkler team can give some hints on what causes the “Empty Response” in detail.