You have stuff on this piece of glass right here.
There really can be no other explanation since print and copy from the glass is fine. Any drum/toner/fuser issue would be apparent on all output.
If it happens off the glass and the adf it is the scanner (the light bar) but if it is on the glass it has to be on the platten (big sheet of glass) and if only the adf it is the strip of glass (the paper moves and the light stays still)
To see the exact location on the glass where there is an issue (My guess is whiteout or a thumb print) lay the output faceup on the glass exactly how it would lay in the document feeder. Exactly to the left of the line defect is where the residue is on that strip of glass.