Export audio to .mp3 and audio won't play

Using Audacity 2.1 on my Mac. Edited a podcast and it plays fully in Audacity as .aup. When I export it as .mp3, only certain portions of the project play. I used recorded audio for the majority of the podcast from a handy recorder. When inserting voiceovers during editing, I recorded directly into the mic. on the computer. Only the sections I recorded into the computer mic playback when I listen to the .mp3 version.

Any ideas what I can do to get all audio to play?

Audacity doesn’t make a 2.1. There is a 2.1.0.

When you are sure you have 2.1.0 from Audacity ® | Free, open source, cross-platform audio software for multi-track recording and editing., check that you did not mute any of the tracks. Muted tracks are not exported.