I was tracking CTA Bus #147 at home to make sure that I would leave my apartment on time to catch the bus and that's what I came across. I wasn't at the stop to confirm whether this was an actual extreme case of bus bunching or just an error in data. Based on my personal experience, CTA route 147 gets bunched frequently, despite being an express service for the most part.
Apparently, this was not the first case of extreme bus bunching. A similar case has recently happened in Seattle and reported on a blog.