Playback choppy whenever there's a harmony

Lately, I've noticed that whenever I'm trying to create a harmony with three or more parts, as soon as it plays a chord, the sound immediately starts getting choppy, stuttering, and distorted. It's not reverb, since I've tried setting that back to zero- and it immediately goes back to normal whenever I cut it down to two notes playing at once. This happens with all instruments, not necessarily the same or different ones.