What does this mean. Is this fixable?
I'm not too sure myself, but maybe you should open it up, unplug the ribbon cable and plug it back in.
If the gameboy pocket is assembled at all remotely like the original brick, you'll have to heat up the ribbon cable and put pressure on the spots that causes the lines to fade away. This is easily done with a low temp soldering iron so long as it's the same material ribbon cable as the brick. Do a tear down and post pictures, would give everyone a better idea of what you're working with.
I think this is a false alarm. Seems that it was a cool effect.