Sorry for not having a proper screenshot or video at hand, but TL;DR: I can see other players' shadows and muzzle effects through walls and ceilings in certain places. For example, on Oilfield, I can see muzzle lights through many of the thin metal sheets on the catways. On B point downstairs, I can see shadow blobs through the ceiling inside the B house.
There are also a bunch of other points where I've noticed this. If this is something that has not yet been extensively reported on, I can start to try and collect screenshots and locations where this is possible.
My specs are Win 10, GTX 1080, Ryzen 2600, latest drivers.