Update Wrong Old URL in SharePoint Alerts on SharePoint Migration or URL Change

$SPSite= Get-SPSite "https://mySharePoint.com/sites/alerts/"

foreach ($spweb in $SPSite.AllWebs)
{
	foreach($alert in $spweb.Alerts)
	{
		$OriginalTitle = $alert.Title
		$alert.Title = "UPDATE: $OriginalTitle"
		$alert.Update()

		$alert.Title = $OriginalTitle
		$alert.Update()
		Write-Host "Updated Alert" $alert.Title "in"$spweb.url
	}
}

$SPSiteURL = "https://NewSharePoint.com/sites/alerts" #Site Collection Url 
$oldrooturl = "https://OldSharePoint.crescent.com" # Old URL of the webapplication
$rooturl = "https://NewSharePoint.com" # New URl for the new webapplication

$SPsite = Get-SPSite -Identity $SPSiteURL 
$SPwebs = $SPsite.AllWebs 

$updated = 0

foreach ($web in $SPwebs) #Get All the sub sites
{
	$alerts = $web.alerts  # Get All Alerts

	if ($alerts.count -ne 0)
	{
		Write-Host -foregroundcolor green "Number of Alerts in: "$web.url ":" $alerts.count

		foreach ($alert in $alerts)
		{
			#preserve & Change the Alert frequency, so that the so the datarow inside is touched by SharePoint API. 
			$Status = $alert.Status 
			$Frequency = $alert.AlertFrequency
			if($Frequency -eq [Microsoft.SharePoint.SPAlertFrequency]::Immediate)
			{ 
				$alert.AlertFrequency = [Microsoft.SharePoint.SPAlertFrequency]::Weekly 
			} 
			else
			{ 
				$alert.AlertFrequency = [Microsoft.SharePoint.SPAlertFrequency]::Immediate 
			} 

			$title = $alert.title
			$alert.title = "UPDATED" + $title
			$alert.Status = [Microsoft.SharePoint.SPAlertStatus]::Off 

			$alert.Update()  #Update the modified values

			if ($alert.Properties -ne $null)
			{
				if ($alert.Properties["siteurl"] -ne $null -and $alert.Properties["siteurl"].Contains($oldrooturl))
				{
				$alert.Properties["siteurl"] = $alert.Properties["siteurl"].Replace($oldrooturl, $rooturl)
				}
				if ($alert.Properties["mobileurl"] -ne $null -and $alert.Properties["mobileurl"].Contains($oldrooturl))
				{
				$alert.Properties["mobileurl"] = $alert.Properties["mobileurl"].Replace($oldrooturl, $rooturl)
				}
				$updated++
			}


			#Reset the Values of alert, back to their original
			$alert.title = $title
			$alert.AlertFrequency = $Frequency 
			$alert.Status = $Status 
			$alert.Update()    

			write-host "Alert updated: " $title
			#$alert.Properties

		}
		Write-Host "Number of alerts updated: " $updated
	}
}