Next/Prev buttons stopped working for the Music app on my 2015 MacBook Air
Here's an imperfect potential solution (depends on how you want to use the feature) – see problem 3 below.

I created an applescript that uses keystrokes to tell apple music to play/pause. This way, you can just use automator to trigger it based on shortcuts (you can similarly bind fast forward and rewind).

Script is below:

on run {input, parameters}

    tell application "System Events"
        tell application "Music" to activate
        key code 49
        key code 48 using {command down}
    end tell

    return input
end run


Pop this into an automator workflow using the "Run AppleScript" action and you can create a shortcut. I'm having issues doing this now, but it's something you can probably research. I use keyboard maestro, which makes setting up shortcuts significantly easier.

To change to rewind and fast forward, just change the line key code 49 to key code 123 and key code 124 respectively (this is left and right arrow keys)

There are a few problems:


you may want to hide music instead of tabbing back to your original program. In that case, just replace key code 48 using {command down} with set visible of process "Music" to false and it'll hide the progam
you can't actually use the f8 key as a shortcut, but you could maybe bind it to something like command 8. You could also probably use Karabiner to rebind the f8 key to something else
This doesn't really fix the "why" of what's going on. I still don't know what's happening for sure, but it is a way for you to get it up and running (I still think you should try messing around with Karabiner to change the f8 key to like the keycode for play/pause. It may add clarity to what's happening).