The Fortinet Security Fabric must be enabled
FortiGate-6000 and 7000 Session-Aware Load Balancing (SLBC) uses the Fortinet Security Fabric for internal communication and synchronization.
In both Split-Task and Multi VDOM modes you can enable Fortinet Telemetry from the GUI by going to Security Fabric > Settings and enabling and configuring FortiGate Telemetry.
In either VDOM mode, you can also enable the Security Fabric from the CLI using the following command:
config system global
cong system csf
set status enable