Official comment
Because that makes far too much sense. Honestly, I believe it sorts them by date added, but it should be alpha. I'll flag this for review again.
Why my USB disk in the tree under explorer not show the folders sorted in alphabetical order???
I have a lot of folders named as YYYYMMDD (Year-Months-Day) and show in the tree as random order (or some strange order).
How can fix it?
Because that makes far too much sense. Honestly, I believe it sorts them by date added, but it should be alpha. I'll flag this for review again.
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I refresh the subject. Does anyone know how to sort alphabetically folders in explorer tree ??
I've got problem too. Any ideas?
It sort by I don't know what...
Problem has started after instal Sierra High.
To be clear - The sorting in the browser MacBook is correct. But sorting rekordbox browser is wrong. It sort folder by ?? I don't know what. Can someone help me to back correct sorting? Its very difficult to find last added folder!
It's in the list to be corrected within rekordbox, it's nothing to do with your files / folders.
It's nothing to do?
Earlier the tree was sorted by filename. Right now there is a mess. Why does it happen?
I'm not sure, but our rekordbox team is aware of it and will try to address it in a future update.
Our engineers have confirmed that this will be addressed in a future update - thanks for your patience.
I am new to Rekordbox and the closest forum I found about my problem is this. The list of musics on Rekordbox explorer is not ordered correctly. I tried to sort by artist, Track Title and even by File name and none worked.
Here is a print of the screen. It should be sorted by Artist but is not. 
The explorer cannot sort properly, please use the collection.