I’m not sure this four year old thread is entirely relevant to your question… Anyway, you have the music ‘back’, what happened? Did you inadvertently delete something, did you lose it in a crash?
Duplicate players are often a by-effect of importing into an existing project. In this case, the (unnamed) main player maybe doesn’t even have a valid (named) instrument. Piano 1/2/3/4 all have their own part layouts, so it should be easy to see if there’s music in them. If you already deleted unwanted flows, I guess they’re empty now, in which case it’s safe to also delete the (players) Piano 1/2/3/4 and their corresponding layouts.
But if you are unsure if your document is in working order, it might be a better idea to post the actual project here (zip it before uploading), so that we can take a look under the hood.