MDL Drumline Parts Inaudible, HELP!?

I'm writing for front ensemble and drumline, but the tenor and bass parts become inaudible, even when putting new notes in. They played at first, but once I added an instrument change (not my first one) in my keyboard parts, they stopped playing. There seems to be no correlation as to why an instrument change from cymbal to marimba, or from triangle to glockenspiel, would cause the bass and tenor voices to stop playing completely. I've tried making an entirely new score, and the problem still happened when I added this instrument change. Any ideas?