I use whatever the latest version of iTunes is and sync to an iPhone X over my personal Wi-Fi connection. For whatever reason their default sync is very bad. If

I use whatever the latest version of iTunes is and sync to an iPhone X over my personal Wi-Fi connection. For whatever reason their default sync is very bad. If you instead put all your iTunes music in a playlist and choose the option to sync only that playlist it works nearly perfectly. I've been using this method since the iPhone 4s came out and have only had issues syncing maybe once or twice a year. I sync a few times per month.