Looks like this is affecting us too 
Here’s a really simple repro for you. I have a clip of almost silence where the source is 0.6857142857142857 seconds long.
Here’s the source OGG file:
After uploading to Roblox, then downloading it using Chrome Web Tools in the asset page the duration of it changes to 0.687891156462585 seconds.
You can see the difference in audio lengths in Audacity. It looks like Roblox is appending some kind of fade to the audio maybe.
Even weirder, the same audio we uploaded earlier when downloaded is 0.6980498866213152 seconds. So the amount of fade appears random.
Having correct audio lengths is really important for us. We utilise a beat length of silence to allow us to sync multiple audio loops allowing players to make original compositions of loops. Without accurate sound lengths, we aren’t able to continue doing this.
Thank you!