Environment : Instant AP deployment with SSID configured.
Hostname information isn't displayed under Clients section of Instant User Interface.
The Name filed displays different information based on the type of SSID.
For PSK clients (no other authentication along with it) - The hostname is displayed and it is picked up from DHCP option sent by client.
For MAC Auth / 802.1x /Captive Portal clients, username used to login is picked up during authentication and displayed.
In all scenarios; the information is provided by the client to be displayed by the interface.
For PSK clients; confirm if client sends DHCP option 12 by taking a packet capture on the client.
For Captive Portal clients / MAC Auth / 802.1x; confirm if client has passed authentication. If client hasn't passed authentication; then it's expected to have "Name" field blank.