I can also confirm that this behaviour...looping updates...also appears on a mid-2010 MBP running OS X 10.10.5 . I'm not familiar with the setup of this MBP but the only thing shared between all these machines is the wifi network...on a Time Capsule, purchased in September 2016, running on a 5GHz network. I'm wondering if there's a setting there that might be involved with this condition.