"But you may also notice that there is a strange vignetting effect at the top and bottom. This is more obvious in the sample images further down below. This effect is only partially related to the lens itself, but the camera also plays a role in this."
But the lens is not producing it... The fault solely lays with the Sony APS-C E-mount cameras.
"On Sony APS-C cameras (notably the A6300, which we used for testing here), the sensor is deeply recessed - see below. The problem is that extremely angled, out-of-focus light-rays are partially hitting the "walls" of the sensor housing, causing the top/bottom vignetting in the highlights."
Notably the A6300? All Sony A6XXX, 5XXX, A3XXX, and NEX models all have the same "fault" in their design. "Notably" means "in particular" or "especially", and then the use of that word in regards to the A63000 is misplaced... All E-mount APS-C cameras are affected in a similar fashion with such large aperture, wide FOV lenses.
"Most likely, this effect is limited to Sony APS-C E mount cameras but that's nothing that we can guarantee."
You can guarantee that this effect is not present with Fuji X-mount cameras, as the sensor surround has been designed without this issue.
Reviews on Fuji cameras bear that out:
Canon EOS M cameras also do not have the Sony sensor-surround issue, so won't cast such a shadow either.
Nikon's Z50 sensor surround also has a rectangular "recess", but appears to be less deep and better designed. My guess is that it won't show a similar issue, but indeed "we can not guarantee" that.