Bear with me, I'm no tech but.....I can BBQ pretty good. I'm assuming you've reset connectors on left side of driver board including the 2J12 as those are the ones I think may be responsible for power/ ground for solenoids. Page 25 of the manual shows a good schematic of colors for flippers etc with org/vio being for the left. There's also a relay on board contained in lil box near 2J12 connector that sometimes has issues.

Reset that whole side as well. Then check again, then next thing I would do is try and eliminate the possibility of pf/cabinet issues and do a jump from left flipper board pin to rt flipper connector socket (you'll need something to act as a pin in the connector and put an alligator clip on it.) You may devise another way of making a secure connection, this just works for me. An insulated Alligator clip will help insure your not touching the adjacent board pins. The connector can be left off as you don't care about any of the other solenoids. Check results and then reverse to Rt flipper pin to left flipper connector socket. Note results.