I encountered this many times, I believe the same issue is preventing any interaction beyond the plane of any piece of foliage, as I was unable to receive a blood transfusion while standing inside one of the large fir trees. Issue was fixed when I walked out. Similarly, any items dropped underneath a bough of any tree or bush are unreachable, even in cases where I am in direct contact or even clipping through the object with my camera. Neither vicinity nor looking-at looting works.