The code sample below will show machines that have duplicate GUIDs in Active Directory:-

function IsDuplicateGUID
{
    # Should expect 1 if no duplicate exists
    # Returns $true for a duplicate
    param([string]$ObjectGUID)
    $Count = Get-ADComputer -Filter 'ObjectGUID -eq $ObjectGUID' -Properties Name,ObjectGUID
    if($Count.Count -gt 1) {return $true} else {return $false}
 
}
$Computers = Get-ADComputer -Filter * -Properties Name,ObjectGUID
foreach($Computer in $Computers){if(IsDuplicateGUID -ObjectGUID $computer.ObjectGUID){$Computer.Name + ' ' + $Computer.ObjectGUID;}}