There are three coil lugs. One is for hold power. If the hold power is out then flutter will occur as the flipper charges, the high power cuts assuming hold power will hold it. But them the flipper starts to drop so EOS hits and tells the CPU to send another high power burst. This continues until you release the flipper button.
I would check if one of the three wires came loose off the coil. I would bet that the coil, itself is not the problem, but it could be. First check the wires. If it looks ok I would check voltage with the dmm on the hold and ground lugs while the flipper button is held in during game. This will tell you if there is hold voltage. Should be 8-10v or such. No voltage indicates a wiring or board issue. You could swap coils as LTG suggested or just reflow the solder at the wires to the coils.