Are any plugins in play that may not releasing correctly when you render?
Have you added any new plugins around the time the issue started?

Also, on initial Render do you see the popup afterwards that asks to test the file?
Just wondering if that is hiding somewhere and causing the second render issue .. a long shot, I know

And lastly, where is your Temp Audio Directory located?

Make your sound your own!
.. I do not work here, but the benefits are still awesome