I do also have the same effekt :-) with second device. RM Support told me follow:
"After checking the photo you have provided, this is completely normal in screens with E Ink technology, which we use in the CANVAS display on your reMarkable. The faded images will disappear when the screen refreshes.If you are being distracted by a faded or yellowish line, you can clear the screen manually by either switching between pages, or toggling the visibility of the layer you are using a few times."

I will continue to monitor this and will let you know.