Can't add Apple Classical music to Apple Watch

I have an Apple Watch SE running watchOS 9.6.1 and an iPhone 13 Plus running iOS 16.6.

Using the Watch app on my phone, I am able to add music to my watch by selecting Music > Add Music and selecting albums from my Apple Music library ... unless It's a classical album, in which case the add (+) button on the top of the album page is greyed out. It's the strangest thing and seems to have just started happening with the 9.6.1 update.

See attached screenshots, which show the album page in the Watch app for one album from Apple Music, and one from Apple Classical (which is also in my "main" Apple Music library.) The add button is greyed out for every single classical album in my library, and present for every single non-classical album.

I've restarted both my watch and my phone, reset sync data on the watch, removed all music that had already been on my watch (including several classical albums which were added previously with no problems) and logged in and back out of my Apple ID.

A search for this issue in these discussions and on Reddit doesn't turn up anything, which makes me think that it's a problem with watchOS 9.6.1 as it's only been out for a week or so. But I'm wondering if anyone else has run into this problem, or if there's anything I can do that I haven't done already.