Quoted from Gatinho:Most theories posted here were that the ball is getting hung up on a lip from an uneven magnet where it penetrates the play-field, but as you can see in the attached photo, it's not hung up on any lip.
The reason for this is that powering down the magnet would not normally be part of the ball search procedure and if the magnet was locked on you would blow a fuse, transistor, etc. Not ruling out that possibility but it would be more likely the vibration caused by the solenoids firing is releasing the ball.
If you turn the game off when the ball is locked does it release?