After creating a Vegas project and trying to render it, I continuously only have sound the first 40 seconds or so. After that, nothing. Once in a while (but not always), I have the same problem in the program itself, where I will lose sound after around 40 seconds. Pausing and starting fixes the problem or moving the cursor also helps, so I am assuming the two are connected, but I've absolutely no clue why and have not been able to find a similar problem around.
One thing I've noted is, that I never had this problem rendering smaller scenes separately. It is only when making larger projects that the problems occurs.
I am rendering in MainConcept AVC/ACC as Internet HD 1080p mp4 and all the files used in the project are mp4s as well.
I have yet to try another format, but I will let it render during my workday tomorrow on another setting.