It might well be the lyrics you are adding to the file. Are you following the Lyric Tag Guide?, it may be that you are adding extra stuff in the Lyrics Tag which is causing Roon to ignore it. I just tested it and it worked for me.
As a test, try following the guide, and just type a couple of lines of nonsense and see if Roon picks it up.
I just tested it moments ago replacing an existing lyrics with nonsense and it worked.