Sometimes it happens, that the maintenance tool of Qt is running and running and nothing is happening. It stucks at 99% and I waited hours of hours. In my case the following helped me to overcome this:

1. Open Windows Explorer and enable the following option: show hidden files and folders
2. Be sure that the maintenance tool is not running in the background (TaskManager)
3. Now clear the following folder (it should contain ‘remoterepo-*’ – folders)

   C:\Users\profile-name\AppData\Local\Temp\

4. Finished. Now open the Qt Maintenance tool and try again to update or modify your packages.