Don't blame the camera too fast. Describe your film holders and shooting techniques too. That's a BIG light leak!
... oh, and tell about your film. Did it come from a sealed box? How did you load your holders? There are many potential sources to consider.
I got leaks like that from reinserting the dark slide too roughly and unseating the holder from the camera.
Are you pulling the film with the holder in the camera? If so, I'd suspect your unseating the holder in that process. Does Shen Hoa have graflock sliders or is the 405 under the GG held by springs?
When pulling and reinserting the dark slide, put the thumb of your left hand in the middle of the ground glass and grip the back of the camera with your fingers. Press firmly. Remove and insert the dark slide with your right hand while holding the ground glass in place in this manner. Develop this habit, and you won't lose pictures from accidental light leaks. Light moves very quickly and sneaks through tiny cracks like magic. I learned this from experience!
The Shen Hao has a interchangeable bellows, make sure that the front and rear of the bellows is securely mounted.
Having said that, like the others I think it looks like an issue with the film back.