Audio cutting out at the end of videos

Hi everyone, I'm hoping to get some help on an issue I had yesterday. I took about 9 3-5 minute videos yesterday, and at the end of each (the last 20 seconds) the sound mysteriously cut out and the rest of the video was muted. I have no explanation for this. I tried playing the video on multiple platforms and they all had the sound muted on the last portion of the video. Anybody have a fix? Can I get the last 20 seconds back? Thanks!