Your problem is probably due to the fact that the default browser or some related service is not white listed in the launcher. When the device hits the captive portal it needs to launch a browser in order for the user to login and if the browser is not permitted to run by the rules setup in the launcher then it will fail.
in the meantime I have solved by myself...browser was not the fault.
I have whitelisted this Android native components:
that did the trick.
maybe also helped this: