There are 2 type of (erroneous) lines on screen:
the sharp figured that cover exactly 1 or more lines of pixels full across the display
the „moving“ type that pop up and disappear at various vertical positions in quick sequence.
The latter can in fact be a sign of a worn (or badly placed) display ribbon cable, usually at the main circuit board end.
Sharp missing lines are a consequence of missing contacts of the display screen itself and are almost impossible to repair. There is a description by someone who tried to fix this and gave up in the end here on the board.