Playing MP3 files stops

I have a folder of MP3 files that were recorded via Audacity and then exported as mono MP3 files. Using the Box Android app, some of these files play as expected, meaning that they complete and then the next file plays. However, others do not exhibit this behavior. They may play and then stop at the end with the message, "Preview unavailable" so that the next file does not play, or it may halt playing abruptly in the middle of the song, and then you have to go to the app and tap Play again. And this is not just an issue with the Box player. I have had the same issue with other players, like that in File Manager +. I suspect the reason is that all of these web players use the same engine, and there is something about these Audacity files that it does not like. Do you have any idea as to why this happens and how to fix it, as it is very annoying and inconvenient?