Perhaps you have moved to a new library or computer in a way which means that you've downloaded Apple Music (DRM) copies of tracks that you had previously purchased. See Hide and unhide music, movies, TV shows, audiobooks, and books - Apple Support to make sure that your past purchases aren't hidden. If you have some hidden purchases try removing the download that you have, unhide the purchase, then download again.
Recent builds of iTunes have also worked badly with File > Burn Playlist to Disc. Use the right-click option on the playlist name in the sidebar instead.
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