Songs on iPhone suddenly greyed out, "not currently available in your country or region"

I've seen this asked many times but have not seen a solution.

I recently updated my iPhone 13 to 16.3.1. Things seemed to be OK, but last night I noticed that most of my music is greyed out. I get the error, "This song is not currently available in your country or region."

The library on my music server (a 2015 Macbook Pro running 11.7.4) is fine.

I am not an Apple Music subscriber. About 90 percent of the 2 GB of music I carry around is legally imported from my CD collection. Most of the rest is songs I purchased from Apple, which appear to be still available on my phone.

I have tried signing out on both devices and signing back in. I also have repeatedly reauthorized my computer. This seems to start a cycle where the grey songs completely disappear, then return, but still grey and unplayable.

I suspect I am going to have to delete everything and start anew but would like to avoid that, especially because I am not sure that will actually solve anything.

Has anybody successfully dealt with this?