Certain unit of NIC-510/810-4xGigE-PT are being shipped with the bridge configued as "failed-closed". This is usually noticed when the ProxySG is configured inline and when ProxySG lost power and the trunk connection between proxy and the upstream is disconnected as the result of the "failed-closed" settings.
To changed the setting back to "failed-open", we need to change it via CLI
ProxySG#(config bridge) edit bridge_name
ProxySG#(config bridge bridge_name) mode fail-open