I also have this issue on Windows 10 edition. No matter how many times I try, it gives me this error. It gets to "Initializing upload" without the uploading bar showing, and then gives an error usually within the next 6-10 seconds. I just activated the Realms free trial yesterday and uploads didn't work then either. I also tried using a wired connection, but I don't think it did anything besides maybe giving an error faster.
K V
I also have this issue on Windows 10 edition. No matter how many times I try, it gives me this error. It gets to "Initializing upload" without the uploading bar showing, and then gives an error usually within the next 6-10 seconds. I just activated the Realms free trial yesterday and uploads didn't work then either. I also tried using a wired connection, but I don't think it did anything besides maybe giving an error faster.