What I feared happened. The gopro mount is way to fragile for my setup. This is my first attempt for a more robust version. Printing right now, so no endresult yet to review.
As forces on the gopro mount can become intens, especially on my setup I opted for 100% infill (lazy as S3D doesn't support mesh infill and didn't bothert use Cura) as I found lower infill can cause unexpected gaps in the infill that can cause cracks.