I have a couple 70's Williams EMs that have done that before.
Either replace the EOS switches or clean them up real good with a file. Then, do as Zacaj recommended and try setting them to open minimally (maybe 1-1.5 mm) when the flipper bat is fully up.

What was happening with my games, was that when the EOS would open up, the coil goes to the low power "hold" function. If I held the flipper up to trap or catch, a fast-moving ball would naturally bend the flipper bat down a little since the coil was now at low power function. After the bat bent down far enough, the EOS switch would close back up and re-engage the high power function of the coil and effectively "pogo" the ball back upwards with notable power. You want to experiment with the EOS switch to try and minimize that "pogo" travel. You are shortening the stroke, so to speak.

Lee

Or, you could try practicing soccer style traps to stop the ball dead on the bat