With the flipper coming back down) that is a double winding coil the second (hold) winding is maybe compromised. Have you rebuilt the flippers lately? Vid offers a good thread on that. also try out Pinball Wiki. Take some good pictures for us.

the sound issue is likely a loose connector

Half the fun of pinball for me is figuring out how to fix things and fine tune the mechanics.

I would suggest that if your sound works intermitantly or in test that your speaker connections are right and you have another problem.

If you get sound out of your speakers the connection is good. look elsewhere. your boards are tested so I suspect it is another connector issue somewhere

I have heard the phrase "divide and conquer" applied to troubleshooting. test things to find if they are working to trace the problem, rule out what is working and move on.

Study Pinballwiki for an explanation of boards.

Fixing the flipper was easy once you found the problem