I was having some trouble with my iCloud Keychain today, so I called Apple. They had me log out of iCloud and do some other things only to find that there was no problem, it was in the implementation of Two Factor Authentication. After I did all the steps that they asked me to do, my Mac was a mess. I had three copies, for some reason, of all of my contacts. My Photos won't sync to the iCloud Photo Library anymore. I lost all of my Mail Rules and Preferences and for some reason the Guest Account Login was showing when I rebooted even though I disabled it years ago. At any rate, after the three hour disaster I got things back to normal, with the exception of the Photos issue and Two Factor Authentication. I have 2 Macs, an iPad and an iPhone. In the past, when I would log into the iCloud website, I would get a notification on all of my devices to allow me to log in. I would then get a PIN and log into the site. After clicking "Allow" on any one of my devices, the notification would go away on the others. After today's call with Apple, when I click "Allow" on my iMac, which is the computer that I logged out of iCloud today per Apple's request, I get a PIN, just as before, and log into the site, but the notification won't clear from my other devices. I tried logging in on the other devices and it works just as it's supposed to, but not on this one iMac. So after I use the PIN that I get on my Mac and access the site just fine, I have to go to one of my other devices, tap Allow and then just ignore the PIN that it gives me. This isn't a problem, but I don't know why this isn't working correctly. Now if I go to log in to the site from the iMac and then click Allow on my iPhone, the pop up notification does clear from the iMac like it's supposed to. Any ideas?