Power BI "Sign Up" fix
Power BI is an optional Office app that can be added from the office.com apps tile page, by clicking All Apps, and Get More Apps. When you search for Power BI and add it, the app will ask for the user to Sign Up, and not have their UW credentials added to the app.
The fix for this Sign Up error is to goto https://powerbi.microsoft.com/en-us/ in a new tab/window and Sign In. This should then carry over to the tiles page app, and Power BI will then be signed into with UW credentials when opened from the apps page.