I have a 4-port 5200 that recently started experiencing graphical glitches with certain games. Moon Patrol and Space Invaders, for instance, start normally but become corrupted as the game progresses. Pitfall appeared as a jumbled mess and can't even be started. The 4-port is one that has been modified to accept the VCS adapter.
I also have a 2-port 5200 and tried both Moon Patrol and Space Invaders on there and both work fine. Pitfall, as expected, doesn't work.
My phone is dead at the moment so I can't share images of what's occurring but I will update as soon as I can. If anyone has any ideas of what I can check in the meantime, please let me know.