I had this problem 2 years ago. Even though your connectors look good, try reseating them anyway. I did that and my sound came back on.

I also had an issue where a ground wire on the speakers broke. Soldered back on and it's as good as new.

I had a similar issues with my JP last November. First my sound would go out and randomly come back in the middle of a game but be out of sync with the game. A day or two later it was completely gone and would not start at all.
Long story short, a cap on my power supply had leaked and eaten the trace beneath it (I believe it was C2). I ended up having Chris Hibler repair my board with all new caps and connectors. I believe he had to repair a trace as well as it was eaten through.
If you didn't remove the cap, you would have never seen the damage.
The thread I created when I had the issue is https://pinside.com/pinball/forum/topic/de-jp-power-supply-issues
It might have some other helpful information as well.