Plays from iPhone Not Syncing to Mac Music Library

The Music app on my Mac serves as the hub for my overall music library, and I have several smart playlists that are built off of when certain tracks were last played. As such, knowing the last played date for my songs is important! Unfortunately, my iPhone has recently stopped reporting music plays back to my Mac, under any circumstances. A song gets played on my phone, my computer never finds out. (Note that I am not using Apple Music, but I do have an iTunes Match subscription.) This started about a week ago from the time of this writing-- I was looking to see if there was some sort of OS or other software update that might have corresponded to things breaking down, but there doesn't appear to be anything on the mac side. Maybe on the phone side, but I can't easily find my phone's upgrade history.

I hunted around for people with similar issues, and one thing that came up over and over again was to make sure Home Sharing and iCloud were properly setup on my devices. My Mac, indeed, did not have Home Sharing turned on for it-- but I don't think it ever did, and I've always been able to sync my plays before now, so I'm not entirely sure this is to blame. Nevertheless, I turned it on, and it did not solve the issue. Testing on this sort of thing always takes a little time, as I am used to a system in which the two devices only update plays once a day-- the first time you play something on the phone, it will report that play back to the Mac, and sync up anything that hasn't previously been synced. If you keep playing music, those plays won't get reported until the next day, and so on.

Weirdly enough, the two music systems are talking to each other: if I play a song on my Mac, it turns up on the Recently Played playlist on my phone. Similarly, if I create a new playlist on my phone, or add songs to a playlist on my phone, those changes turn up on my mac's Music app, as well.

One factor in the middle of all this that I had really hoped was going to help: I upgraded my phone in the middle of all this; I had initially hoped that the new phone would snap everything back into place, but no dice.

Thoughts?