Music not syncing via iCloud.
To sell an old iPod, I tried resetting and erasing it. Accidentally I erased all music from the iMac Air it was attached to. The music then disappeared from my iPhone and iPad Pro. But fortunately, my iMac still had the music on it. But when I turn syncing on, it syncs, but after that the music just doesn't appear on any other device.
Rebooting, logging in and out of iCloud hasn't solved the issue .....