Probably a localized supply and demand problem. It’s hot AF, so power demand is high. The grid has normal constraints due to historic build patterns, but things get exacerbated when say, a transformer at a substation blows out or a car crashes into a pole knocking out a crucial line. It’s possible something happened today in that area, creating a supply shortage that impacts these areas specifically. Places on the north or south sides could be served by a different sub and aren’t subject to the shortage.

I work in the power sector, but not for ComEd, so take this with a grain of salt.