same problem, drop the lid the wifi cuts out, solution
plastic folder, cut a piece of plastic 4 inches x the width of the keyboard, place it on the track pad area, works a treat, a trackpad and palm guard may do the job too.
but for a new high end item its not acceptable, a software or firmware solution may not be available, it could well be the magnetic closure interfearing with the wifi module i.e a design issue.
Every other laptop in the market allows you to close the laptop and still be connected to wifi, the surface book has no reason to be different,