Fix for static horizontal black lines?

Hi,

I have a 50PUS8015/12 that is showing black horizontal lines every fourth row of pixels, except of the first few cm on the screen. The lines span over the whole panel, and are visible the most on the right side:

Re-seating the ribbon cables to and from the T-Con Board did not change anything. I also tested the TV with only one of the two ribbon cables connected to the T-Con board.

With only the ribbon cable going to the left side (2) connected the right side is black and the left side white:

With only the ribbon cable to the right side (1) connected, the left side still is white but the right side shows colorful lines and appears like a broken panel:

When both are connected the issue with the right side of the panel, except of the lines is not visible:

Is this likely due to an issue with the panel, or could it be caused by something else?

Thank you for any help