On the topic of how the flipper might be causing issues here, make very sure that any diodes soldered on the coil (or on the board the flipper coil is triggered from if they’re not on the coil itself) are good and connected well at both ends. When the coil is released it generates a high voltage spike in reverse that can cause all sorts of havoc without the diode, whose job is to short that spike back through the coil rather than the rest of the circuitry.