To be sure what kind of tags you have written in your *.m4a files, could you please open one of this songs in Mp3tag and then press Alt+T (extended tag view windows).
Please attach a screenshot from this window in your answer.
To be sure what kind of tags you have written in your *.m4a files, could you please open one of this songs in Mp3tag and then press Alt+T (extended tag view windows).
Please attach a screenshot from this window in your answer.