Huge bug in 3.1.0

I just updated Audacity from 3.0.5 to 3.1.0 and opened a mp3 song.
I played it back and noticed it sounded mono even though it was a stereo track.
I saved it as flac, opened it with VLC and it sounded mono there too.
I opened it again with Audacity to check if it had 1 or 2 channels and it had 2.
Basically the new version ignores stereophony and treats all tracks as mono.
I installed 3.0.5 again, did exactly the same thing and I could no longer reproduce the issue.

Thanks for the report! It’s been logged here:

We’ll fix it ASAP.