How do I stop this happening?
I have 1 copy of each song in iTunes but after a sync my iOs devices will have 2 copies of each track.
Not every album. sometimes it goes away & affects other albums. sometimes there are 3 copies. (rare)
iMac, OS X Yosemite (10.10.5)
You could try the following all-purpose steps for dealing with erratic device or sync behaviour (including the troublesome greyed out tracks and/or dotted circles of stalled transfers). They assume that all of the content you want on the device is in your library ready for restoring. If it isn't see Recover your iTunes library from your iPod or iOS device first. I would also recommend you copy everything out of the camera roll if you haven't already.
Use an encrypted backup (*) if you want to preserve passwords, Wi-Fi settings, web history and health data where appropriate. I also suggest syncing with a selection of playlists (unless you're using iCloud Music Library) rather than manually adding content as, if nothing else, the process above is easier to do if you ever have to go through it again.
(*) The downside with backup encryption is that if you forget the password when you need it again, which could be years later, you may need to invoke a workaround to turn off encryption as shown in Re: disable encrypted backups, which can only help if your device is in a state that can backup to iCloud, or runs iOS 11.
For added security you might also want to make an independent backup to iCloud and/or archive your current backup before you start.
tt2
duplicate songs in ios
