Neogeo 6 Slot weirdness....

Hi.
I got a 6 slot that have a rellay strange behaviour….
It works with some games while on some Others it won't and gives graphics error...this in all slots.
For example puzzle bobble works fine while neo turf master doesnt.
https://youtu.be/Bhm04r-vbmg
https://youtu.be/hJ2cq1090v4

I see that the problem is related to the upper board, since i used another upper board and this problem doesn't appear.

I've never seen such a problem.
Someone knows what the problem could be?

6 slots are finicky, just confirm everything is clean and then clean again. Also look for any cold solder joints or corrosion underneath the top board.

If the problem doesn't come from the games and isn't solved by cleaning:

I'm placing bets on some lines of the P bus being cut or stuck.
Does the display change if you touch the pins of the chips on the left and right of the slot where the game is inserted ?