The music editor which especially shai use to create music, has this bug since the patch:

Changing any Volume of a note causes the note and multiple neighboor-notes to go completely mute.

Putting the note back to normal 127 volume wont fix it, only deleting all bugged notes and re-write them works.

So... you cannot change volume of notes at all,

not with a new composition nor with one written before the patch. they are all screwed up. Pls fix what you broke !