Android MediaStore query don't find any m4a audio files

on my device and on all testes emulated devices, I can handle an m4a audio search of the mediastore the right way. One of my beta-tester told me, that on his device it is not possible to get m4a Audio files in response of mediastore query.

Is it possible that some manufacturers do not recognize m4a audio files and they are not referenced in mediastore?

How can one solve this problem?

Uri uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
String m4aDir= "%" + dir + "%";
String[]   projection = new String[]{
                    MediaStore.Audio.Media._ID,
                    MediaStore.Audio.Media.ALBUM,
                    MediaStore.Audio.Media.ARTIST,
                    MediaStore.Audio.Media.DURATION,
                    MediaStore.Audio.Media.TITLE,
                    MediaStore.Audio.Media.DATA,
                    MediaStore.Audio.Media.TRACK,
                    MediaStore.Audio.Media.YEAR,
            };
String[] selectionArgs = new String[] {m4aDir};

Curosr cur = getContentResolver().query(uri, projection, selection, selectionArgs, sortOder);