Ok, thanks again for the great feedback Yasothon,
In short, Samsung has some strict policy for battery optimization and one of the things that they do is to, cut sometimes the wifi/3g connection of the watch. So when this happens, some issues occurs with the weather.
We're almost ready with an update solving these issues and there also will be an option to enter your location manually.
Do you have the weather displayed at least one time? If so, then the problem is with the internet connection.