Outlook Keeps Asking for Microsoft Office 365 Credentials

Outlook 2016 asks for my Office 365 credentials whenever I open it and at random times when it is open.

It does this on my work computer and my home computer. My work computer is only connected to my work Exchange account, and my home computer is connected to my work Exchange account and my Outlook.com account. It repeatedly asks even though I am logged in when I open any other Office application. Furthermore, it says I am logged in when I check File->Office Account in Outlook. All of my email accounts remain connected even though it keeps asking me to sign in to Office 365.

I keep Outlook open at work, and sometimes at home, and when it prompts for this, it steals the focus, and it is greatly annoying. I close the dialog instead of signing in when it prompts, and File->Office Account still says I am signed in.

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