I had the same exact problem on my Solar Ride.
The target bank had a different coil on it to what the manual specifies so I thought it was that but in the end all I had to do was polish the plunger and clean the sleeve.
I think that with 5 targets to reset the target bank coil is on the brink and a small amount of drag is all that is needed to stop it resetting.
Mine has been going strong for over 12 months now so problem solved.

Thank you so much Boots, you were spot on! I cleaned the plunger and sleeve with metho and lots of dirt came off but it still didn't have enough power to lift the 5 targets. I knew I was on the right track because with the playfield inclined it had the power to lift them one time...I used silicon spray on the metal moving parts and now it works every time. You're a legend! It's great to meet someone else with a Solar Ride also!