Run the display monitor-link group group-id command and check the State field in the command output.
An uplink interface Down event may be caused by a link failure, a unidirectional OAM connectivity failure, or an OAM connection setup failure. If the uplink interface is a Smart Link group, the uplink interface is considered faulty only if neither member interface is Active when the Smart Link group is enabled or if both the member interfaces are Down when the Smart Link group is disabled.
Run the display current-configuration interface interface-type interface-number command in each member interface view.