You can clear all the unauthenticated NCP connections from the list using the Clear unauthenticated connections on selected servers option in Actions drop-down.
In UMC, click File Access Protocols > NCP.
Click the Search icon and specify the server name.
or
Click Browse, select Server Type to list their associated servers. Select the required servers from the list, and then click APPLY.
Click NCP > Connections.
Click the Actions drop-down and select Clear unauthenticated connections on selected servers.
In Clear all unauthenticated connections, click Confirm.
You can follow the same steps to clear all connections. Click the Actions drop-down and select Clear all connections on selected servers.