Quoted from zaphX:
A little additional info - I was adjusting that mech last night because the tips of the fork were coming up through the playfield when retracted.
After putting it back together I noted the fork would not retract. Upon examination I noticed a wire to the smaller coil (the one which pulls the release lever) had broken off. I soldered it back and the problem resolved.
Exact same had happened to me. Both solder points were cold, of incredibly poor quality. Pulled the original solder and resoldered the cables, all good now.