This basically fixed my problem on my Galaxy Watch, thank you very much, although I did have one more oddity. When I converted to Celsius, the Today section switched to small negative numbers, like it converted the previous celsius temps as farenheit and converted them again. I then pressed the refresh button at the bottom, while still in Celsius, and all the temperatures were correct celsius. Then switched to F and everything, including Daily, showed the correct temperatures.
@userNHNgpcREFG have you tried the steps recommended by SpaceMoose?
Had the same problem. Had to do a factory reset and reinstall my apps. But did not update the weather app. Turned off auto updates. Now my weather works. I just have to remember not to update weather app.