When there are active sessions on the targets discovered by an iSCSI discovery sendtarget address, you see these symptoms:
Resolution: To resolve this issue, manually terminate the active sessions before removing the discovery address.
esxcli iscsi session list esxcli iscsi session remove --name=<target_name> --adapter=<adapter_name>esxcli iscsi adapter discovery sendtarget remove --adapter=<adapter_name> --address=<IP_address:port> --forceFor additional information see How to remove iSCSI targets on ESXi