You nailed it- the same file exported, when I import it back in, the stereo imaging is still there. So... what the heck is happening to it when I play it from another source?
I've tried multiple apps for playback, and it's always mono, so I don't think it's the app that's playing it that's the problem. OK- as I'm typing, I tried something new. I played it from my phone, and it's in stereo. On my computer, it's in mono when played with multiple different apps. Is this maybe an audio interface setting issue?