Dear support,
I have the same issue since I bought a new iPhone X, previously I had iPhone SE, with no problem with synchronizing my music. When I get the new iPhone X, I did a back up of the SE phone and sync with the new X phone. Everything got over, contacts, apps, photos but no music, and the sync ended up with an error. After I tried to do the separate sync of the music and after I plugged in iPhone X I got this message: the iPhone could not sync because the session failed to start.
I literally tried everything, all is up to date, I removed the previous back up I authorize my computer, I tried this on Mac and Windows computer as well. I reboot my iPhone. Only thing I did not do is the factory reset. But as I read below, the ones they did the back up first then factory reset it solved the sync, but as soon as they put the file/back up on the phone the issue appeared again.
This brings me to the end of it where only problem is probably some corrupted file, setting which gets over when you do the full back up, so even if you do the factory reset, and fix the sync, after you put this all back to your phone is not working again.
Could you please find out what part, setting or file could cause this and how to fix it?
Thank you very much