Track volume keeps resetting itself
I was having this same problem and I think I figured it out. You have to click on ‘Editor’s button’ which is the scissors cutting the sound wave, which should open the MIDI region menu at the bottom of garage band. The make sure your track is unlocked, and then click on the little button just above where it says MIDI Region that looks like three tiny sliders or dots with lines coming out of them. That should open your MIDI draw area where you can not edit the volume and such. From there, edit your volume in the draw area, then fine tune it with the slider located on the track. Make sure when you're done adjusting you lock the track before you press play or it will reset again. It may take a few tries where it does reset a couple times before it sticks, but now, you should be able to get it to stop resetting for you.