Slow and inconsistent music transfer from Logic to iPhone

For some time now there has been a disconnect between Logic-Music-iPhone. Perhaps I should say it’s really between Music and my iPhone as my songs from Logic get to Music with no problem. But when I try to send it to the iPhone either via Sync or just dragging it from my songs (AAC format) list in Music directly to the iPhone the results are hit and miss. And also it take so long to get just one track to transfer, I seem to recall it being much easier and going in much faster years ago. 

I freely admit that it might be something in my system but I’d really like to hear from others what their experience has been and how they accomplish the transfer. 

[Re-Titled by Moderator]