One or more files were not exported

I'm having a severe issue with Rekordbox which started last week. I currently have version 6.5.2 installed on Mac OS Big Sur (11.5). Last week I've added a couple of new tracks to my collection/playlists. When I synced to an SD card that I've been using for while already, I got the message "One or more files were not exported". A file was created in the Documents folder which contained a list of all of the newly added tracks. There were no further error messages in the file.  

Strange Without You (Sunnery James & Ryan Marciano Extended Remix) Tensnake, Dáramólá /Users/janvanryswyck/Jan/DJMusic/Current - Groove Low/Tensnake, Dáramólá - Strange Without You (Sunnery James & Ryan Marciano Extended Remix).mp3
On The Beach (Kryder Extended Remix) York /Users/janvanryswyck/Jan/DJMusic/Current - Groove Low/York - On The Beach (Kryder Extended Remix).mp3

Automatic (The Aston Shuffle Extended Remix) Tensnake Automatic (The Aston Shuffle Remix) /Users/janvanryswyck/Jan/DJMusic/Current - Groove Low/Tensnake - Automatic (The Aston Shuffle Remix).mp3

When I looked on the SD card, I noticed that the mp3 files were added, but that they were 0 bytes. Does anyone have any suggestions on how to fix this issue? Any help is very much appreciated.