I would say that 16388 was the cell PID which is now no longer running.
When the cell stops, we issue a close socket call to the OS and so it is the responsibility of the OS to close the socket. I have seen it before (on rare occasions) whereby the OS has not closed the socket and so only option is a server reboot.
It is possible to enable lowlevel network communication trace in the cell, but that would only confirm we have issued the close socket call. We will not be able to see what the OS then did with.
You may wish to bring this to the attention of your OS administrator.