I had a similar problem which was mainly solved by pulling the lock bar and separating the "leaf springs" that get compressed when you push the fire button. Mine were all kind of pressed together with no separation. I bent them so they were just slightly apart when the button wasn't pressed, but would touch when it was.
Solved the issue almost completely. I say almost because randomly I had the issue reoccur twice, once as a result of not having the lockbar back on while the glass was off and play testing the Bicycle Girl ramp I just reinstalled and once randomly another time and in that case I think as Yipykya mentioned I don't know if I remember the music changing for Crossbow.