Hi Alex, Welcome to pinside!!
Intermittent problems can take a little more persistence to fix because we're never 100% sure when they're fixed.
With that said, Inspect and diagnose this circuit with Alligator clip jumper wires
http://www.planetimming.com/Pinball/troubleshooting/EM%20Troubleshooting.pdf
http://www.pinrepair.com/em/index3.htm#features