AppleTV stereo audio only plays from left speaker.

I have a 5.1 stereo system with a Yamaha receiver and I just noticed that things that should be in stereo (or mono) are only playing out of the left speaker. Not the center or left and right. Audio from my cable box is correctly sent to the center speaker, when I watch movies on the AppleTV that output in 5.1, they play correctly in surround sound. It’s just on things like YouTube or TV shows that should just be standard stereo it all plays out of the left. I tried the audio settings in AppleTV but there aren’t many options to change and they didn’t do anything.