Virb GPX Files inconsistent - first especially

As Virb Edit does such a rubbish job of managing the hundreds of video files that I generate a month I have decided to not use it for importing but iumport the video file and the GPX myself into one location so that the video and the metadata stay in the same place.

Looking at my ride today the second video file of the series is synced really well:

https://www.youtube.com/watch?v=8j54nEUNrFM

This was created by importing the video into Virb Edit then the GPX file with no synchronsing done at all. They both start at the same time - whjich is what I want.

The first file is not synchronised though, there is a discrpency of about 6 seconds.

Why is this?

Is this perhaps the file that is created when I turn the camera on instead of when I start it? If so where is the gpx file that is created to match the first video file?

I have only looked at this from one ride so this could be an anomoly.

Anyone else found this?

Thanks