Just a little fyi...

If something is selected, only what is selected will be exported.

If you have only 1 track selected, then only that track will be exported.
If you have only 1 clip selected, then only that clip will be exported.

So depending on your needs, Be sure to select the tracks you want included, and select in the timeline the section you want to export.

Finally, if you are going to export the whole project with all tracks, make sure nothing is selected, or make sure everything is selected.  I usually make sure that nothing in the project  is selected when exporting the entire mix.

hth...