Paper transport at 600 PPI and the head acting at 1200 PPI ?
Or an interference related to that.
Not that that guess brings a solution :-)
Edit: well, it could be related to filth on the servo sensor on either the paper transport axle (lines parallel to the head movement) or on the head sensor that reads the ribbon along the width (stripes parallel to paper transport). But that would be happening with any paper at 1200 PPI.
Then there is the unlikely event that copying the media preset corrupted right on the number of strokes or alike. Maybe the original media preset isn't used by anyone on 1200 PPI and a bug is never reported. Try it without copying, make more copies and compare with a copy of another media preset.
met vriendelijke groeten, Ernst Dinkla
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