Virtua Fighter 1 Tilemap error?

Retro Muel

Newbie
Credits
13CR
Hi folks.
I have a sega model 1 Virtua Fighter PCB that's developed a fault recently. I've attached pics to demonstrate. As you can see it only affects the top portion of the screen, and only when polygons appear there. Is it some sort of tilemap error maybe? My memory test and TGP tests come back fine, and the board is working perfectly apart from this. I've tried using contact cleaner and reseating all the boards etc, even switching out the power supply for a high end Mean well unit, but it's still there unfortunately. Does anything obvious stand out to anyone?
Any help would be much appreciated.
Cheers.
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