Why does my iMac constantly ask for iCloud approval?

At least once per day my iMac has a pop up reading "iCloud Approval Required This Mac is still waiting for approval by another device." The choices of responses are "Not now" and "Continue". I have Continued about 20 times, I go through the rigamarole of entering my Apple ID, wait for the text on my phone and enter that number. Many times. I think this started with the latest update.

The only devices I use my iCloud for are the iMac and iPhone, and I even recently turned it off on the iPhone because of this. Has anyone dealt with this successfully? It's driving me crazy.