When exporting a selection (different parts of an image exported as a whole): depeding of the file format, lines appears (white for JPG, or grey for TIFF) around the frames.
Those lines doesn't always appear around the same frames (sometimes on the left, sometimes on the right side of the image).
E-Paper_ANP0834_1_5z2.tiff
E-Paper_ANP0834_1-5c.tiff