iTunes doesn't load compilations onto my iPhone

I have a huge music collection. I paid extra to get the 256 GB Flash on my iPhone 7. I sync it with a Mac Mini.

I used to have a MacBook Pro, but it died. I removed the Flash drive and mounted it in an external USB case. Just now I copied over the Compilations folder from the old iTunes Media to the new one, then synched my phone with iTunes.

iTunes on the Mini displays my compilations correctly, but absolutely none of them got loaded on the phone.