I've been getting back into Jazz recently and replaying the SP levels, but I noticed something that's bugged me for a long time--when I beat a level, the victory jingle never plays, it just has an awkward silence. I remember it worked properly waaaay back when I first played the game, but at some point it stopped. Is there some way to fix it?

As far as I'm concerned, it's a JJ2+ bug. There's also this thread in which this problem is mentioned. Not sure if there's anything you can do about it other than switching to vanilla JJ2.

I don't think this is a Plus bug. I remember this problem happening before Plus existed, and in the thread you linked there are other people also saying it happens in the vanilla version (at least 1.24--I would check if the bug was introduced in 1.24, but I don't have access to a copy of 1.23 at the moment. I don't know where my old JJ2 discs are, so all I have is the GoG version.)

EDIT: Someone in the other thread mentioned the jingles do work in full-screen. I can confirm that fixes the issue, but it might still be worth fixing it for windowed mode in Plus at some point.