This could actually be a bug report, i lost a whole day today troubleshooting this, hope it helps someone....
I use an external SSD (Sandisk Extreme SSD 250 - new model) and i use it for other programs and equipment, other than pioneer, so my music is sorted in folders, which i then drag and drop in rekordbox to create playlists. It works fine and on my thumb drives too, for years now. The problem occurred after 5.4.1 update, when i dragged a folder into rekordbox to create a playlist, rekordbox createda a playlist and everything worked fine, the music was usable, but in the folder it created another file, a copy, or a clone of the original, like this - original: (example)
Danny Cruz - Life Saver (Original Mix) [Onako Records].mp3
and the created, cloned, file (example)
Danny Cruz - Life Saver (Original Mix) [Onako Records].mp3Danny Cruz - Life Saver (Original Mix) [Onako Records]
- the created file was used by rekordbox, the original was not touched, hence it doubled my collection size, and this was the same if i imported only one file, or a whole folder, in collection or in playlist, always the same, a clone of original was made and used. And this problem was ONLY on external ssd, the thumb drives worked OK, no problems (did not double the files).
The SOLUTION for me was to install 5.4.0. which works fine, no problems with ssd at all - so i call it a compatibility problem, or something, hope pioneer fixes it, and i hope this helps someone ;)