You could also try this program. I have put back your MIDI output instead of the debug statements.
It does not use the sensors at all. For a test, it just sends some MIDI messages to turn notes on and off. Delays between them for testing so you can hear what is happening.
If you look at the commands in the program, does your MIDI device play what you would expect?
harp_test_3.ino (1.38 KB)