[EDIT: I figured it out! The two MIDI tracks were set to the same MIDI channel, but had different Fader values. I could click on one Fader and adjust the loudness of the other track, and vice versa. I guess that is normal behavior? In any case, I know what the problem is, and how to work around it. Thanks for your help! Can skip the below if you wish, I’m leaving it up just in case I need to refer to it again later.]
I am writing this real time as I trouble-shoot.
Yes - MIDI track, not instrument.
I checked the Project Browser immediately after opening. There are no CC messages at the beginning of the project. Only Velocity and aftertouch. And the “CC7 Main Volume” automation lane is empty.
The Fader immediately after opening is set to 59. Piano sounds too soft.
I clicked the fader - the MIDI piano immediately got louder to where I think I mixed it at. Nothing else changed, regarding all the things I mentioned above.
If I close down the project and reopen, we are back to step 2 again - sounds too soft. Occurs whether I resave before closing down or not.
I’m glad you found the solution. Yes, this is the issue. If you route two MIDI Tracks to the same Channel (the same MIDI Port) both are sharing the sama data like CCs Values, Program Changes, etc. This is useful when you want to put Drums to multiple tracks (Bass Drum, Snare, Hi-Hat, etc.).