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Sorry, you're going to have to try narrowing it down manually as the log is only kept for tracks that failed when the export completes. Create smaller batches of playlists to pinpoint which track(s) are causing it to stop. It could be due to a corrupt file or un-analysed track.
If it's taking that long to export, the write speeds of that USB drive aren't very good; you may consider using a higher quality drive.