iPhone XR ios 18.5 - "This item is not currently available in your country or region"?

I manage my music using iTunes 12.13.7.1 on a Windows 11 machine. Recently, I am receiving the 'this item is not currently available in your country or region' when attempting to play music on my iPhone. Affected songs were imported from CD or purchased through a non-Apple site (.mp3).

I've done the following:

• Restarted the phone
• Restarted the computer
• Deleted a sample 3 affected albums from the iTunes library and synced. Them re-imported the 3 albums and synced. No improvement.

I have no interest in subscribing to Apple Music or iTunes Match. This is music I have already bought and paid for and should not have to pay additional monies just to play on my phone.

There are no syncing issues on my iPod Touch 6th generation 12.5.7, so this is clearly an issue with the phone.

How can the syncing issues on my iPhone be corrected?