Watched folder 'Automatically add to iTunes' creates duplicates. Solution?

Hi there,

I have the following problem: when adding my ripped CD-collection to iTunes by dropping the media-files into the watched folder 'Automatically add to iTunes', iTunes creates duplicates/triplicates (or even more). The size of my collection forces me to store media files on an external storage. I have tried importing whilst storing my library on an external USB-drive and whilst storing it on my NAS (my preferred option). Both scenarios result in a bonanza of duplicates. My library counts over 35.000+ files in lossless quality and my last attempt results in approximately 95K duplicates. The duplication occurs in the library, not with the files it is referring to. In other words, multiple library entries referring to the same media file. Here's the importing proces, step-by-step:

1. I organize my media in an 'import' folder, with resides in the root on the same volume where I want iTunes to store my media;
2. I delete the library files (a.o. iTunes Library.itl) where iTunes looks for them;
3. I connect to my NAS through AFP and create a new, empty folder named 'iTunes';
4. I start up iTunes holding the option-key and choose to create a new (fresh) library in the newly created folder on my NAS;
5. I check wether a new *.itl file is created;
6. In preferences, I make sure that in advanced settings the 'iTunes media folder location' points to the same newly created folder on my NAS;
7. I then move the entire import-folder containing my media into the 'Automatically add to iTunes' folder and wait for iTunes to populate the new library and move the files into the designated media folder;
8. I do not interfere this proces until the 'Automatically add to iTunes' folder is empty, the new library is populated and all my media files are moved to the media folder.

This procedure resulted in up to 100K duplicates in different tries. Every time I deleted the library and started all over with a pristine new and empty library. Every time with the same result. I also varied the procedure by dragging smaller portions of the import-folder to the watched folder, but this also resulted in duplicates, though not as many as with the full import.

As I do not tell iTunes to import files twice, I do not understand why this keeps happening. I think this should work flawlessly and iTunes users should not have to resort to 3rd party solutions to 'dedupe' their libraries. Does anyone have advices how to remedy this situation?

Many thanks for your advice(s),

Jannem

My setup:

• Mac Mini (2009) running MacOS El Capitan (version 10.11.6) and OSX Server (5.2)
• iTunes (version 12.7.2.58)
• Synology NAS (DS412+) connected through AFP
• All devices connected via Gigabit Ethernet, Airport Extreme

Note: I administrate my Mac Mini server (running iTunes) via Apple RDC. I have done the import-move from (a) the Mac Mini (without RDC and through RDC), (b) from my MacBook Pro and (c) from the file manager within Synology DSM 6.1.4