iTunes version 184.108.40.206 is writing "work name, name and movement" in audio files.
sample captured in mediainfo
©wrk : Work
©mvn : Work Name
©mvi : 2
©mvc : 3
Apple says : "Tag for movement name is 'MVNM' and movement number is 'MVIN’".
I have seen this in m4a, I suspect it is the same for mp3.
Please check this and update in mp3tag.