I had 7 files that I recorded in Audacity and converted to mp3 where there were instances of skipping and gaps. When I opened the original Audacity file and played it back I found places where it sounded like multiple version of the same audio being played out of sync.
I downloaded the latest version of Audacity 2.1.2! One of the files now played perfectly in this version. But it didn’t help with any of the other files.
Pirhan Dastoor suggested deleting one of the tracks as follows:
1) With your file open in Audacity, click on "Edit" on the menu bar, then click "Select" and then "All".
2) Click on the down arrow on the left corner of the screen on the track. It should be right above the "Mute | Solo" button on the track. It looks like an arrow pointing downwards, when you click on it, a drop down menu should open. Select "Split Stereo to Mono".
3) Now you should see two tracks, try deleting one of the tracks and playing the audio to see if it's in sync. If that does not work then press undo and try deleting the other track and check to see if that resolves the issue. If it still does not work then don't save the file.
I discovered that you can delete a whole track at once after it is split into Mono by clicking on the X to the left of “Audio Track” in the box to the left of the track you want to delete.
It DID seem to make a difference which track I deleted. Sometimes the top was better, sometimes the bottom.
This was very helpful.