This bug still occurs in the newest hotfix update 1.19.21. However instead of going to the upload screen and having an empty bar below the "All Done!" screen, it instead goes to the "Applying Packs" screen (shown below) and then the "Some of the Selected Content Could Not Be Applied" Screen.
Update on this issue: I am still having problems uploading addons to my realm on 1.19.41. When I try to upload an addon using the edit feature, it says "Applying Packs" then "Error: Some of the selected content could not be applied."