I am having the same issue. In the preview the video and audio is synced up correctly, but when I render it 3 minutes of my video pieces disappear, but audio keeps going and ends correctly.
Can you provide a little more detail:
I am on a Laptop, Lenovo. The file is fully synced before I export it. What it is doing is taking out about a 3 minute chunk of video (when rendering) and then just leaving the final screen of the video up while the audio finishes playing. In the edit mode and in the preview just before exporting, everything lines up appropriately and it doesn't cut out the 3 minutes of video footage.