Erratic behaviour of Synching music from iMAC to iPhone XR.

Thank you for the initial advice. I had already completed the steps listed in your link article but have repeated them anyway. The problem remains, certain playlists and individual songs set up on the iMac Music do not transfer when hitting apply and then sync within Finder. These songs play ok on the Mac. I am using a USB connection between devices. (My Mac is up to date with software, macOS Catalina, 10.15.7, my iPhone XR is also up to date iOS 15.6). What seems to happen with some transfer attempts is when I hit sync is a little bit of activity for a few seconds in the status bar below the selection window in Finder, then nothing and no transfer detected to the iPhone. This is obviously different to when songs do actually transfer and you can even see the titles of the songs being transferred in the text below the status bar. Examples of songs that do not transfer are encoded as mpeg audio, but others that do include AAC purchased tracks. Some of my tracks in my library have of course been ripped from my own former CDs. Over to you!

Thanks, eventually got round to this, and basically only AAC encoded music files will sync between the iMAC and the iPhone music apps. This means somewhat laboriously recreating my transfer playlist by checking the file format on each track and converting as you have shown me when the mpeg format does not transfer. Interestingly, it only takes one rogue mpeg in a playlist collection to block the transfer. I have also discovered that you have to leave the playlist selections ticked in the sync settings because what happens if you only want to update one playlist and think you need the other's unticked....whoops, the unticked ones disappear from the iPhone. As you say this seems to be a transfer problem, because the mpeg song tracks all play quite happily on the iMac and my older mini iPad.....not sure why Apple have designed it this way, but at least it now works and I can enjoy editing a new playlist all encoded as AAC!! .