I can't seem to get Dynamics to work.

I'm currently importing a .mid file and trying to add dynamics to it, but whenever I set one for a group of notes the playback will not follow them and will instead play every note in the same dynamic. I figured it might be a velocity issue, so I tried setting it to Zero for the entire section I'm trying to add dynamics to, but nothing seems to be working. Perhaps my issue is whenever I change the velocity to zero it always changes it back to 64?

If you're willing to look into it, attached to this message is the song I'm trying to adjust dynamics on. Specifically, the "Piano, pitch channel 3" section. Thank you for your time and have a good day!