If you say that you leave those playlists playing for hours, it doesn't seem that strange that the software sometimes repeats one of the songs, especially if it has played all of them until that point.
There isn't such an option, but, then again, the software plays the songs in order or in random mode, so unless you play the playlists in random mode, the software can't possibly play one song twice or more (only if it's finished all of the songs in that particular playlist and started playing the entire playlist again).
Hope this helps. If I didn't understand your problem correctly, please send a detailed email to firstname.lastname@example.org
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