Quoted from BigAl56:I hope you are not running sandpaper through the playfield switches. Those are gold plated and should be cleaned with paper like a business card.
Possible the eos is not adjusted properly and is opening too soon. The EOS should open at about 80% of the stroke. The EOS should also open before the upper flipper activation switch closes. (Break Make). Check the EOS adjustment by pushing in the flipper link with your finger and not by turning the flipper itself.
All the switches involved with the flipper (eos and cab) are high voltage, not gold plated