This worked for me i don't know if is going to work with you, but this is what i did. And sorry my English, is not my primary language.
If you changed where the Windows App are installed like me just do what i did, my currently drive (D:) the one i have only for games.
Windows App are installed in C: that's default but you can change it in settings.
I uninstalled the game, that you can do from the start menu.
I changed back the drive to C: in settings like my drive for installing apps.
Windows Store must be close cause is going to prevent you the deleting of this folders.
Then i found the Windows App folder and the WUDownload Cache Folder in drive D: and I deleted those folders. (Probably just deleting the WUDownload Cache can fix this too.)
Then i changed back the drive to D: and started a new download, the download started with no error and so far i have 22.49 GB of 49.09 GB. (i have a **** low internet.) XD
If you have other drive you can change the drive and check if the download start, i didn't have much space in drive C: to just do this and check if worked or not just changing drives.
I hope this work for you.