Music ratings (only some) on iPhone 12 disappear

I listen to my music on my iPhone and rate the tracks. To do this, I have a smart playlist for all unrated songs. Recently, some of the ratings of songs that I have rated on my iPhone, go missing. In iTunes on my Mac Mini also also does not show as recently played. This is only happening to specific albums, not all albums. Strangely, this only affects albums purchased in December 2024 (not ratings were captured), but not those purchased earlier in 2024 (all ratings were captured).

After I plugged my iPhone into the Mac Mini, I tested by rating a few of these affected songs and syncing, and then the iPhone did indeed sync back to iTunes. I then tested by unplugging my iPhone, rating one of these latest purchases, and then plugging back in and syncing. This successfully also synced successfully.

What could have caused this? It is very frustrating because I had recently listened and rated quite a large number of songs, and this has all been lost. I would hate for it to happen again.

I have an iPhone 12, iOs 18.1.1, and the latest version of Music (not sure how to find version number, but the App Store indicates it is updated). My Mac Mini runs on Sequoia 15.1.1 and Music 1.5.1.24.