Hi there,
we are having the same issue with the AppAuth Library.
The only solution that I've found so far was a workaround from the side of the Login-Page.
An added, static "You successfully logged in" page with a "continue" button after the login.
Gary Archer from authguidance.com made a blogpost "iOS Code Sample Overview" (cannot post the full link here, the forum forbidds it) where he showed his solution.