Jumping frame on GoPro + Zenmuse

I was shooting on my Phantom 2 with GoPro 3+ and Zenmuse HD-3D today and had problems with the vertical framing suddenly jumping. At times it looks mechanical, but mostly more camera-related. Here's the footage:


Anyone had similar issues? Any thoughts on the cause? I had temporarily removed the optional interference board in and out of the gimbal - could this have caused something?
 



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