Re: Splash-page doesn´t appear with iPhones since IOS 11.3 and 11.4 with Cisco ISE Guet-WiFi
if you are using a self-signed cert in ISE, your users might be getting a warning on the cert before joining. a good test would be to try to join via an android phone that either has never joined and or delete the ssid (and cert) and see if it give you a cert warning.
If it does not get a success reply, the captive web portal browser will appear which will redirect to either Meraki's Authentication splash or a customer Radius Authentication service.
So if your walled garden is allowing access to *.apple.com, the Apple device will think that you have access to the internet without authentication and continue as normal. However the user won't be prompted to authenticate until they try to visit a non https site.