Exported MP3 plays one channel only

A project plays only one of the two tracks. I exported as mp3 and the resulting saved file plays only one channel. The speakers work, and the graphic shows both tracks, no irregularities, but the playback level graphic only shows one channel. The size of the mp3 file is normal as if it has both tracks. Another project I exported just minutes before, during the same session, does play both channels. The two projects are hours one and two of a radio show. Hour one mp3 broadcast normally, hour two only one channel/ Both projects are still open in Audacity just as they were, never closed. I’m hoping to fix the missing channel before closing. What is wrong?

I’m keeping the Audacity session open and the computer on for several days hoping to fix the project. Does no one have any thought on this subject?

It isn’t just the exported file, it’s the project itself that plays only one channel.

Does a screenshot help? https://www.dropbox.com/s/gh8c9nh311jw81v/Audacity%20session%20screenshot.JPG?dl=0

The only things missing in the shot are that the playback readout is missing the left channel when playing, and I change from Micophone to Stereo Mix when necessary.

I’m wondering if I accidentally changed something on settings that I’m not noticing.

The pan slider should be in the center,

, it’s hard right …

Wow, that fixed it. Thanks! I must have hit it somehow. I haven’t learned about the pan slider, what it does.

I’ve been caught out like this too - and that’s why I wrote this Proposal: Missing features - Audacity Support