The CAS is running on an SSP or ISG appliance.
The LAG interface is created on the ISG appliance, for example, interface 9:0 or 9:1.
Under the CAS's Settings > Network, the interface 9:x is not visible on the management console GUI.
On the same SSP/ISG appliance, there is a proxy application running and there is no issue, where the interface 9:x is visible from the proxy management console GUI.
On the ISG CAS, one more step needs to be run: to enable the interface 9:x from the CLI.
(config)# interface 9:0 enable
If you have another LAG interface (eg: 9:1), please run the command to enable the interface.
(config)# interface 9:1 enable