FlexConnect is a wireless solution for branch office and remote office deployments. It allows APs to switch client data traffic locally and perform client authentication locally when they are disconnected from the WLC.
For WLAN A to work in FlexConnect mode and WLAN B to work in local mode, the APs need to be part of a FlexConnect group with proper WLAN-VLAN mappings. This ensures that the correct VLAN is used for each WLAN, which is essential when the APs are operating in FlexConnect mode. References: CCNP Enterprise Wireless Design ENWLSD 300-425 and Implementation ENWLSI 300-430 Official Cert Guide.