I think its a bug in their driver for vNIC. Its not a VMware issue. I doubt VMware support can do some help since its an appliance, its good to give a try by opening a VMware SR.
2017-06-14T19:18:50.405Z| vcpu-1| I125: Msg_Post: Error
2017-06-14T19:18:50.405Z| vcpu-1| I125: [msg.log.error.unrecoverable] VMware ESX unrecoverable error: (vcpu-1)
2017-06-14T19:18:50.405Z| vcpu-1| I125+ vcpu-0:VERIFY devices/net/vlance_shared.c:1104
2017-06-14T19:18:50.405Z| vcpu-1| I125: [msg.panic.haveLog] A log file is available in "/vmfs/volumes/586e86b7-dfcbabed-e5ac-001c7f3f20ea/Untangle/vmware.log".
2017-06-14T19:18:50.405Z| vcpu-1| I125: [msg.panic.requestSupport.withoutLog] You can request support.
2017-06-14T19:18:50.405Z| vcpu-1| I125: [msg.panic.requestSupport.vmSupport.vmx86]
2017-06-14T19:18:50.405Z| vcpu-1| I125+ To collect data to submit to VMware technical support, run "vm-support".
2017-06-14T19:18:50.405Z| vcpu-1| I125: [msg.panic.response] We will respond on the basis of your support entitlement.
2017-06-14T19:18:50.405Z| vcpu-1| I125: ----------------------------------------