No, I do not think it is a bug. I am staying in an apartment at the moment with exactly the same issue. I think a few have given you less than 5 stars for overall experience. Where I am staying right now there are some issues not covered by "location, cleanliness, arrival, communication" and the like; things that could lead to a lower score for overall experience.
The property I am staying at has flowing reviews and is booked up 6 months in advance, but the host does not have superhost status simply because the overall experience ratings are below 5.
In my case it can be noise issues, layout, very low ceilings, lack of natural light.