It may be that the defective board came with a broken track. It happens that the stubs come broken. You can make a jumper and run it as an extension through the common line of the loop. This is a temporary solution, as artifacts will appear in the future, there may be a break. The most difficult thing is to bare the loop, remove the mask and glue from it. You need a microscope. Then solder them in a neutral place with overlapping and gluing. Tin solder won't hold. Oxidation+small drop will not hold mass. You will also have to check after soldering the tracks for short circuits. Multimeter to help
And why make a studio display? It's a waste of time. It's easier to buy a new, high-quality, stylish monitor from another company.
Dang that’s getting far too technical for me 😅 so, I have an iMac Pro and had the opportunity to pickup a second one with a couple defective parts, but mostly functional, and for very cheap. I had seen Luke Miani’s DIY Studio Display (on a standard 5k iMac 27” not Pro), and I thought it would look awesome having two matching displays for the setup. I know, certainly not the “easiest” option, but this conversion board was $150 and the iMac was $500. (CAD) so much cheaper than the $2000 studio display, and the matching is kinda cool 😎 but first I figured I’d try and fix up the iMac Pro and see if I can get a second working machine.
It seems as both the original cables, and the cables in this conversion kit cause the issue. If I understand you correctly, it’s the cable that loops around the perimeter of the screen, flat, black, and glued down or something? Not sure if this is something I can send away for repair, as the soldering is a no go for me lol.
Maybe a new screen would be the best way forward? Still much cheaper than a new display, and again, I realllly like the matching lol