Hi ,
Whenever VSA- appliance virtual machines experience connection loss to their iSCSI connections, they are designed to reboot . Please perform the following steps:
1 . Disconnect the virtual nic of the VSA node and reboot the node to see if it is the problem with the network connectivity on the node having the issue.
2. Check if there is no physical network mis configuration.
If you are unable to find the cause of the issue please contact VMware Support, they might help to replace the faulty node with no data loss.