I have the Rotatrim M 54" model.
Only recently I noticed large scrape marks that travel in the same direction as the cutting head. A close inspection revealed a gizmo attached to the cutting head to prevent overweight paper from being used, it is basically a metal bar... that has somehow worked its way loose, so it touches and scratches the paper as the head is pulled across.
Until I have the time to take apart and figure out how to re-mount this gizmo, I'm using a piece of tape to hold it up.
I have scratched several prints from what I thought was sliding the paper under the plastic bar ... I will try the suggestion to use tissue paper, though that might make it difficult to see properly.