It can depend on type of file. Some file types will reserve space on the drive. And due to the way LW downloads not in sequential order, you might have parts of the start of the file, some parts in the middle & the end of the file; so the file tells your HDD that the file size is a certain size from start to finish. This is usually true for video files.

Torrent files will 'always' reserve space on your drive even before the file has started to download.

Are you sure the files play from start to finish, nothing missing in the middle? And also includes the very end part?

The best way to restart a download is to search it as you did originally with the LW search function, & then using the 'Get More Results' tool. The 'fix stalled' tool will only search known hosts of the file that are online at that time. And since people's ip addresses might be dynamic & change, 'fix stalled' only has limited abilities. I suspect 'fix stalled' only searches for the hosts the file was previously downloading from, but as suggested, if such hosts have fresh ip addresses or are not online, that will render 'fix stalled' as having limited success abilities.