Here you can see, that the file is local on my HD (green check mark from Dropbox) and that the root folder in Rekordbox corresponds:

So all my tracks on Dropbox are also local on my hard drive. But the Dropbox folder structure has somehow changed. I can still play the tracks in my Rekordbox, but as soon as I export them to my USB stick it says that the files were not found.
I changed the folder settings here:

And I went to "File" > "Display all missing files", but it doesn't find any. So within Rekordbox everything looks just fine, only the export doesn't work.
Any ideas where to start?
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Here you can see, that the file is local on my HD (green check mark from Dropbox) and that the root folder in Rekordbox corresponds:

Can you please file an inquiry ticket here and our support team will gather some additional information to assist you in resolving this issue.