I’ve noticed that this has been a recurring issue for many years now so i apologize for bringing it up again, but my hearing is better in my right ear than my left and use the Windows volume balance to level it out, but when Audacity is launched it is reset.
I use Windows 7 64bit, i’ve tried Audacity versions 2.1.1 and 2.1.0.
I presume you have read the other posts about it already, but if not, try choosing a different host in Audacity Device Toolbar, or go to the web site of your computer manufacturer and see if there is a later audio driver for your computer model.
If that does not help you can open Windows Device Manager and see if there is a previous set of drivers you can roll back to.
Changes for Audacity 2.0.3 probably have caused this issue (at least for MME or Windows DirectSound) but for most people the changes were beneficial, ensuring that the Audacity volume sliders and Windows volume sliders moved in parallel with each other. So if you did go back to 2.0.2 you may or may not have other volume issues.
Bit of an update, when i try to record it asks me to select a recording device even though one is already selected or to choose a project rate, doing either lets me record, then when trying to playback it asks to select a playback device or rate, selecting one counteracts the other so i couldn’t for example playback and record at the same time.
I went back to version 2.0.2 and that’s resolved everything, volume balance sticks even on MME and there are no problems with my devices.
Random suggestion but i’m sure it would have been in the program already if it was possible, an option in preferences for Windows audio balance, if a user has this issue of the balance being reset we could tell Audacity what our balance is and it can set it to what it already is when launched. It’s obviously not fixing the problem but it’s a way around it.