Actually, apple devices try to reach out to captive.apple.com once you connect to a WiFi network, which automatically creates a HTTP GET request and therefore your splash page should kick-in. If this doesn't happen, it might be due to several reasons such as a firewall blocking access to that page or similar. I suggest you take a pcap and check what's happening when you client associates to a SSID. ... View more

Are you sure you haven't changed the MX from Bridge to NAT mode or turned on DHCP on any of the configured VLANs? Also, the MX has the ability to relay DHCP requests, so while you haven't changed anything on the MX, but yet it a network DHCP server might have come up. I suggest you take a pcap and analyze this in more details. Here is a link for DHCP relay on the MX: https://documentation.meraki.com/MX-Z/DHCP/DHCP_Services#DHCP_relay ... View more