Harmony out of wack

I dont know what the heck happened, but ever since this morning, when I try to have two notes play at the same time on a midi instrument that is CAPABLE playing more than one note, suddenly some of the lowest playing notes just dont play. I dont know what is causing this, but it is forcing me to put in so much extra work to get the chords that I want, for something that was so simple in the past. PLEASE FIX THIS!!!

teffyjeffy about GarageBand, v2.2.2