I've got a MacBook Pro (mid 2014) and Bluetooth earphones (TaoTronics TT-BH07). I'm usually good with noticing changes with audio in general. A few days ago, I've realized that sound was a bit like balanced to the right. I've thought it was just me or my ear, or the song that I was listening. Then it kept, and I went to the audio settings just to be sure. Here is (approximately) what it looked like:
I've changed the slider to center, and the problem went away. I've thought I've accidentally changed it somehow.
Today, I've started listening music and immediately realized that sound was again off to the right. Went to settings and it was again biased right like the screenshot. This time I'm 100% sure that I haven't messed with it accidentally.
I've fixed it again and currently I'm having no issues. But why would this keep happening? I'm on macOS 10.12.2.
UPDATE: Yes, I've seen Audio balance is being changed randomly in a MBP retina 15'' mid 2012 but my case seems to be isolated to Bluetooth Audio in particular. Never had (or at least realized) that this is the case with wired earphones or internal speakers. In addition, I use the same Bluetooth earphones with my iPhone and Apple Watch, and I'm not having any problems with them.
Best Answer
This is not the solution to the bug, however, there is an open source MacOS app that is a workaround. It watches for balance changes and centres immediately.
Disclaimer: I made the application. I had similar problems with both Bluetooth headphones and normal headphones.