Couple things to check- If your using the AP as DHCP (Access control>Client IP and VLAN) server the wireless clients are isolated and cannot communicate together, you'll need to use the MX for DHCP and use the external dhcp option. Are the devices on different vlans? If so bonjour forwarding is something to look at. Also on firewall and traffic shaping page make sure layer 2 isolation is not enabled and that your firewall rules are permitting traffic between these devices.
Lastly if all these options check out I would recommend opening a case with support and getting some live troubleshooting help with them.
Knowledge is power