When implementing BYOD solutions using more than one Wireless LAN Controller, WLAN IDs must be kept consistent. WLAN ID is used by ISE in determining which WLAN (SSID) clients are using to connect to the network. Ensuring each WLAN has the same WLAN ID on each WLC is essential for proper operation and security.
https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Borderless_Networks/Unified_Access/ BYOD_Design_Guide/BYOD_Wireless.html