I have the following script that does a continuous ping and reports failures. It works fine, except the loop apparently "suspends" when the computer is locked. I have confirmed this by starting the script, immediately locking the PC, waiting 10 minutes, and seeing how many pings have occurred. It is nowhere near the expected number. What could be the culprit?

Write-Host "Entering monitoring loop..." -Background DarkRed

$ping   = new-object System.Net.NetworkInformation.Ping

$count_up  = 0
$count_dn  = 0
$count_dd  = 0

while ($true) {
    $result = $ping.send("10.1.1.1")

    if ($result.Status -eq "Success") {
        $count_up++
        $count_dd = 0
    }
    else {
        $count_dn++
        $count_dd++

        $this_date = Get-Date

        Write-Host "VPN ping failed at time " $this_date -Background Magenta

        if ($count_dd -gt 3) {
            Write-Host "***VPN is Down***" `a
            send_mail_notification("VPN is Down", "")
        }
    }

    if ($Host.UI.RawUI.KeyAvailable -and ("q" -eq $Host.UI.RawUI.ReadKey("IncludeKeyUp,NoEcho").Character)) {
        Write-Host "Exiting monitoring loop..." -Background DarkRed
        break;
    }

    Start-Sleep -m 250
}

$total = $count_up + $count_dn
$uptime = 100 * $count_up / $total

Write-Host $count_up " out of " $total " pings for a " $uptime "% uptime."