Error code -50 on purchased it i Tunes track, even after following re-download suggestion

I use Apple Music and occasionally purchase tracks from iTunes store to covert to mp3 and listen on my mp3 player. On a few occasions I am stuck with an HLS Media file which won't convert. Reading previous posts and replies, I understand this indicated a protected Apple Music file.

Following advice to a similar query on another thread, I have tried deleting from library, starting again and down-loading from the Family Purchases list in the hope it generates an unprotected file. It does not. When I do this, the newly downloaded files also have HLS media format and I get the -50 error error message when I try to convert that track to mp3.

Usually I can convert purchased tracks to mp3. Occasionally I get the -50 error that i get in this unsuccessful loop of deleting, redownloading and always being stuck with media format set to HLS. This has now happened with at least three tracks, the most recent one being today. In each case they are tracks I have initially Added to my Apple Music Library and subsequently purchased on iTunes store.

Any advice on how to make the files available for conversion to mp3 appreciated, thank you