Upon opening the blizzard game launcher, I experienced a bug where the download speed (updating overwatch) falls to the range of less than 100 bytes per second, if not zero bytes per second. CPU usage SKYROCKETED (I have a core i5 4690k clocked at 4.6 GHZ) to the point where the blizzard update client was using every last bit of CPU available, typically between 75% and 93% CPU usage dedicated to just the blizzard update client. Although the displayed download speed is at zero, the remaining download size continued to shrink until the update finished. While updating, the update client chewed through so much of my available CPU that all other applications suffered. Network speeds were not the problem, as I was consistently getting 250 mb/s download speeds in other programs and tests, and network usage was at 0.01% for a majority of the update.
TL;DR: While updating, the Blizzard update client EATS CPUs and doesn’t use anywhere close to the amount of bandwidth available to it (but still downloads data), while also showing a download speed of zero.