Security Intelligence Events shows https://www.microsoft.com as being URL blocked and classified under Security Intelligence Category as "URL Malware." Is Firepower's Collective Security Intelligence (CSI) URL blocking Microsoft.com?
Remove the user from the administrators list first. It's located here in the menu options:Administration > System > Admin Access > Administrators > Admin UsersYou should be able to completely delete the account after.
I was able to get it to work by right-clicking on the URL in Connections > Security Intelligence Events and then clicking "Whitelist HTTP/S Connections to Domain Now" and "Whitelist HTTP/S Connections to URL Now."