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Only fix that has worked for us so far is rolling back to previous version of Outlook 

Here it is if anyone else needs:

At the command prompt, run the following commands:

cd %programfiles%\Common Files\Microsoft Shared\ClickToRun\

officec2rclient.exe /update user updatetoversion=16.0.8326.2107

Don't forget to disable updates until Microsoft gets around to fixing this.

Outlook - File - office account - office updates - update options - disable updates

Thanks to @Sean Varley &  http://www.brucebnews.com/2017/08/outlook-and-the-never-ending-password-prompt/