One of the recommendations was to try different locations within the attic not just at the existing one. Did you try moving the antenna around and observe where the signals converged? At one attic installation it took over two hours to find the location where all the signals converged.
One of the pitfalls of attic installation is that signals are not that extensive but instead "migrate" to specific spots. In an attic not all spots are equal. The antidote to that is to put the antenna on the roof higher to avoid the way signals are treated within an enclosure such as an attic.
Since it is the south side of Chicago that is being affected by the antenna replacement, are you living in that area?