Does this issue occur on multiple songs or is it just one specific song?
If it's one specific song it will be quite difficult to diagnose.
If this happens every time you mixdown a song then I would recommend creating a support ticket and attaching a system NFO file as well as a clip of the issue you're having.
If you're not sure how to attach a system NFO file, don't sweat it. Just create a ticket and the technician will walk you through the process.