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I would say the problem is possibly macOS Big Sur, which is not yet supported, because it does work:

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Hi,
for me the traffic light functionality only seems to work in Collection. I would like it to work in any playlist. Is that possible? How can I make it happen? Thank you.
Mac version 11.0.1
Rekordbox version 6.4.2
I would say the problem is possibly macOS Big Sur, which is not yet supported, because it does work:

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It works fine for me, 6.4.2 Windows 10. Did you load a track and start it?
it only works in a playlist from your collection but not from a USB drive , isn it?
I want to use my HDD Hard drive with traffic funtion but it doesn t work