After Portal update from 10.3.1 to 10.4.1 some users internet explorer cannot view the web app builder applications.
The home page views fine but opening the application just has the blue background with the wiggly bar chart loading icon.
Clearing temporary internet files and cookies worked for most users, but some had to use a slightly different option.
UN-Check the top item "Preserve Favorites website data"
Then select the Delete button and OK
Then close any open internet explorer windows
That should clear the issue