So I had the same issue with adding the widget and just the clock appearing. I knew it was something to do with the location settings because a few days I was messing with these options to see if I could stop a major battery drain that has been happening on my phone since it updated on 8/9.
As I went through all of the location settings, I of course removed some apps that I did not think needed to be there such as accuweather and weather channel. There was an ambiguous service in the Location area set to High usage named "Unified Daemon" and this is KEY. I had disabled this service, not know what it was.
If you disabled or removed the "Unified Daemon", the weather will no longer show up in the Widget nor update. If you have refresh issues, you need to clear the cache on the "Unified Daemon". If you disabled it, the weather will not work on the widget that came on the phone until you enable it again.
I hope this helps someone. From all of the reading I found, nothing mentions this unified daemon but alas, this is a proprietary service from Samsung that they use for Lock Screen, Home Screen and Proprietary Widgets.