I have downloaded and installed Security Update 2016-002 10.10.5 three times, and it still appears as an available Update in the App Store.
It also appears as having been installed 3 times today (each one of these duplicate updates has its own line) under "Updates Installed in the Last 30 Days" under Updates.
What gives?
MacBook Pro (13-inch Mid 2010), OS X Yosemite (10.10.5)
That usually means that it isn't actually being installed.
I suggest manually downloading this combo update which is supposed to have that security update as well and see if this solves the issue and repairs what might be wrong to boot.
Download OS X El Capitan 10.11.4 Combo Update
Sorry, I didn't catch that you are still at Yosemite! Here is that security update for Yosemite by itself that you can manually install.
Download Security Update 2016-002 Yosemite
Late 2012 Mac mini, OS X El Capitan 10.11.4; Apple Watch, 38 mm silver AL, Watch OS 2.2; iPad Air 2 & iPhone 6+, iOS 9.4
That fixed it!
Thank you, Dah•veed.
The Security Update has disappeared from the list of upcoming updates.
(It still stays 3x in the Recent Updates list.)
Security Update 2016-002 App Store issue
