My Galaxy 4 watch just went through a software update R870XXU1IXK1 and after the update my watch no longer showed the temperature in the weather app as fahrenheit. I can go in to the app settings under the weather app and change it from Celsius back to fahrenheit, but it changes back to celsius after a few hours. I'm not exactly sure when it changes back, it may be when the Bluetooth connection is broken with the phone.
I've tried a different weather app, but the default can't be changed and a different app is useless considering it will not be connected to the tiles or face.
I reset my watch and set everything up. It changed back to Celsius after about an hour and a half. I confirmed that the location is allowed on the watch and the app.
