There's two different problems that can be caused by entering a location such as http://localhost:8080/.magnolia/admincentral#app:doesnotexist

When there's no apps running and you enter a location for an app that does not exist this results in an empty green screen, at this point the shell icons respond either slowly, not at all, and sometimes they work but the shell apps appear left aligned.

When there's an app running,
entering a location with an app that does not exist makes LocationHistoryHandler fall back to default location which is shell:applauncher. Entering it a second time removes app launcher and leaves the faulty app name in the location bar. What happens on the server side is that LocationController decides against this location and wants to go to the default location, but it knows that its already there so it does nothing. The problem with the disappearing applauncher is likely on the client side. LocationController though, should probably set the fragment even when it decides to stay where it is.