Yeah, I recently exported a screenshot and for some reason it left out 2 objects. In the upper right corner are 5 more-or-less identical rooms. The top 2 rooms are missing the desks which are identical objects to the desks in the other rooms. Everything else seems to be there. I was thinking maybe because they were not snapped to grid that the footprint fell outside the bounds of capture, but I checked the snap and they are inside.
In order for the capture to work "properly" with the correct things showing, I set the map to no vision so it will show all the exposed FOW areas and captured it as a player. As you can see, there's not that many objects and there are many duplicates (with different names).
My thought is the image capture thinks those 2 objects are out of bounds for whatever reason. I can't think of any other special relation to the capture area and those 2 objects other than that.