Syncing PC iTunes with iPhone 15 Plus. Certain tracke do not copy to the iPhone.

I have iTunes that works fine on my PC (Windows 11) though tracks have gone missing when I sync to my iPhone 15 Plus. Interestingly enough when I try and play the playlists when the iPhone is attached to the PC, those tracks won't play through the PC iTunes and an exclamation mark appears. Once synced those tracks are either missing or blanked out from the iPhone Playlist. When blanked out there is a message this track won't play because the country or region doesn't support it. This is totally absurd as those tracks have played fine for years on iPods and iPhones and in many instances the tracks are from the same album that have other tracks that play OK. In the Windows File Manager I can see the iPhone library OK and drilling down I can see the individual tracks. If I double click on them, they play OK through iTunes. I can see there are a number of third party apps that say they can fix this sort of problem, however can they fix THIS problem ? It would seem to me many of these iTunes issues suddenly appear after iPhone updates ?