I don't have an interface mixer, so that's not it.

Took a screenshot saved on my desktop, but not sure how to post it on this forum.  Image Insert gives me a request to Enter User URL.

Offset mode?

Sounds like the Interleave on the Master bus is set to mono because your tracks can be mono and still pan. Also you can set the Master to mono interleave and pan. This will not allow panning on tracks, but master still appears to pan (mono signal panning) So, I would use 'I' to open the inspector and look on the Master bus for the little blue light stereo signal button. (blue = stereo, gray = mono). If this doesn't work, use the inspector to inspect the interleave (stereo/mono) of the bus's and tracks. Mono FX as well.

Interleave button was the issue.  I'd swear that was the first thing I'd checked on all channels and that I'd re-checked it.  My serum caffeine level has obviously been too low.

Thanks!

Glad to help! :)