All my magnets work fine on mine. Occasionally a badass ramp shot will go right thru the magnets, most the time it catches it however. If it's once in a while I'd chaulk it up to normal.
But if most the time.... Try flipping your magnet donut coils over the opposite way. Made a world of difference in mine, very noticeable. I think the cores get a bit biased after some time and need a polarity flip??, kinda like the earth!