Here's the exact steps to replicate the problem.
I'm using the latest version of Video Converter.
Load a DVD into the tray.
Open Video Converter and "Browse" to the DVD.
Select 3 chapters to convert.
Select MP4 or MOV output.
Go to Advanced and select Batch > Split.
Start conversion.
Once completed, none of the converted videos have sound.
If I convert one chapter at a time, they do have audio.