Apple has released a small update to iTunes. Version 12.4.3 of the music player and management app fixes a playlist bug related to syncing playlists:
This update resolves an issue where playlist changes made on other devices may not appear in iTunes.
This bug occurred when you made changes to a playlist on an iOS device, and these changes were not synced back to your iTunes library. It’s not yet clear if the update resolves all these issues.
Download iTunes 12.4.3 here, or through the Mac App Store, or the usual way you update iTunes on Windows.