Important update: when ripping the device open to get the ssd out, I have found the cause to the problem (at least on my particular machine). It seems that there is a batch of devices with missing motherboard screws and fan screws, and the screw missing is conveniently responsible for keeping the battery connected to the motherboard. The screws for the fan is also missing, causing it to prop up and press against the display, causing a white pressure mark. This is atrocious quality control on Microsoft's part and I hope this never happens again. If a Microsoft representative could acknowledge this problem it will be greatly appreciated.
Update: the water is actually deeper than I thought, not only is it missing a screw, the screws near the motherboard isn't actually holding anything down. And after prying the motherboard with a knife near the working screws it appears that it takes no force at all to pull the motherboard off through the screw head. This means my problem was not only caused by the missing screw, but it is also the deformation of the back panel which pulled the two remaining screws off the motherboard.
Another edit: after some more research I have found that the screws "missing" from the images is actually by design, and the metal standoffs are actually just for holding the battery and fan board in place. But, the problem persists where the motherboard screws are only held by a metal washer which is welded onto the back of the motherboard, which can snap off the board and render the screw useless and the motherboard free-floating, which is what I found when I opened the machine. From other teardowns I suspect the method has not been changed for the newer surface devices, meaning slight deformation can snap off the screws and might break the device.