I suspect it is one of the trough switches acting up (likely not the trough entrance switch).

EDIT: or like Cody mentioned above a lack of 3 balls.

The two upkickers on the right that serve the KISS and SLIDE shots have separate opto switches. The common elements between those two switches is the opto circuitry and the voltage supplied to that circuitry so the opto circuitry and/or its voltage are possibilities. The other common link to the ball search is that one of the switches that the balls are at when the problem happens may not be working consistently. I would start by checking the switches that the two balls in the trough are activating. It could be a poor connection or intermittent acting switch.

What is your 12volt unregulated measuring?
Do you have ColorDMD installed?

I believe that TP1 is 12 volts unregulated on CFTBL so your 14 V reading is good.

When you make the KISS/SLIDE shot to start the multiball, does the animation come on that says multiball? (or does it just wait for a ball search?).

Do you have a high intensity bulb in the hologram light? There are some threads that say that can cause voltage problems.