The ISCSI target (istgt) has a very low listen backlog. When it first starts or is restarted it is overwhelmed by iSCSI initiator requests; which generates the message "Listen queue overflow: X already in queue awaiting acceptance". If it were to queue them up by having a larger listen backlog it could deal with them in an orderly manner. This behaviour causes the initiator to generate timeout requests.
Listen queue overflow: 2 already in queue awaiting acceptance
Create a Nas4Free appliance with 20 targets and get the initiator to connect to all of them at once. e.g. Press the "Save and Restart" button on the web UI.
The commansd "netstat -LAan" will show the listen max queue length.