Something similar here. I was adding 1.5 inch round, screened vents to my upper supers for ventilation last year. Over winter, they closed them off just like you show in your picture. Only these were completely sealed with propolis, leaving only the kerf in the inner cover for top ventilation.
In the wild, I feel sure the bees regulate their inside space by manipulating their entrance. Hard to say they did it because of SHB, wax moths, robbing, other bugs, mice, or even too much ventilation.....They are being bees, I wouldn't read too much into it...Certainly nothing to be alarmed over.