I have reset the game with the factory settings. Whatever difficulty level (easy to extra hard) I notice the following.
When the ball is launched, the first switch that the ball closes, whatever the switch, lights up steadily the upper "NW" insert which flickers, as the player usually needs to hit the targets to do the same. When the second ball is launched, the lower "NW" is lit automatically after any switch is activated, provided it still flickers. Third ball does the same with the red bottom "NE".
I doubt it is a normal behaviour but in the same time, it seems to be so well organized that a trouble in the switch matrix looks unbelievable to me.
Can anyone give me feedback ?