PVS Target device boot up stuck at 'Starting Windows' forever. Most of the time reboot the problem VM from the hypervisor the VM can boot up without issue. 

Also we could see the PVS Target device boot up stuck at 'vDisk found'

Workaround:
Deploy script to detect and reboot the virtue machines which meet all following conditions:
1. Virtue machine is power on.
2. VDA is not registered to Xendesktop; also it has been more than 15min after last de-registration.  
3. There is no session on the machine. 

*********Powershell Script***********

asnp citrix.broker.admin.v2
$machines = Get-BrokerMachine -MaxRecordCount 800
foreach ($machine in $machines) {
$vm = $machine.MachineName
$powerstatus = $machine.PowerState
$registerstatus = $machine.RegistrationState
$sessionstatus = $machine.SessionCount
$LastDeregistrationTime = $machine.LastDeregistrationTime
$time = Get-Date
If (($powerstatus -eq "On") -and ($registerstatus -eq "Unregistered") -and ($sessionstatus -eq 0) )
{
   If ($LastDeregistrationTime)
   {
     $diff = $time-$LastDeregistrationTime 
     If([int] $diff.TotalMinutes -gt 15)
     {  
        New-BrokerHostingPowerAction -MachineName $vm -Action Reset
        write-host "restart problematic machines.."
        echo "Date:$time machine:$vm" >> C:\restartlog.txt
     }
   } 
} 
}
**********************************************************

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Problem Cause

The log and wireshark traces show that the failing target finished login, got the vDisk information, and started reading from the vDisk by bootstrap. After login, the only meaningful bootstrap function is the Int13 redirector that redirects disk IO to network IO and it's driven by NT-loader. If server doesn't reply to a read request, it will retry 10 times at 5 sec interval and then stop (the OS loading stops). 
So our focus at this point at least should not be on the bootstrap (which is well beaten to be good for the Int13 handler). The question is likely that the vDisk may contain some software that, during NT-loading, its driver is loaded into memory, and in certain network environment (e.g. some traffic hits this device) the driver reacts and cause corruption to the network stack.