This PowerShell code works on PowerShell v1 - v4. It does not run in PowerShell v5 (specifically have tested on Win10 Enterprise x64 build 9926). The PS interpreter freezes with high CPU.

PSClass_Repro_Reduced11.ps1

function New-PSClass([string] $ClassName, [scriptblock] $definition, $Inherit) {
  function property([string]$name, [scriptblock] $get, [scriptblock] $set, [switch]$private, [switch]$override, [switch] $static ) {
    $class.Properties[$name] = @{Name=$name;GetScript=$get;SetScript=$set;Private=$private;Override=$override}
  }
  $class = New-Object Management.Automation.PSObject
  Attach-PSNote $class Properties @{}
  Attach-PSScriptMethod $class AttachTo {
    function AttachAndInit($instance, [array]$params) {
	  $instance = __PSClass-AttachObject $this $instance
    __PSClass-Initialize $this $instance $params # Executing this line - calling this dummy function - is what caused PowerShell to freeze
	  }
	  [array]$params = $Args[1]
	  AttachAndInit $Args[0] $params
  }
  Attach-PSScriptMethod $class New {
    $instance = new-object Management.Automation.PSObject
    $this.AttachTo($instance, $Args)
  }
  Attach-PSScriptMethod $class InvokeProperty {
    __PSClass-InvokePropertyMethod $this $Args[0] $Args[1] $Args[2] $Args[3] # I would love to remove this pointless function call, but then I can't repro...
  }
  $output = &$definition
  $class
}

function __PSClass-Initialize($class, $instance, $params) {} # I would love to remove this pointless function, but then I can't repro...

function __PSClass-AttachObject($class, [PSObject] $instance) {
  Attach-PSNote $instance Class $class
  foreach ($key in $Class.Properties.keys) {
    $Property = $Class.Properties[$key]
    $targetObject = $instance
    $ObjectString = '$this'
    $instanceScriptText = $ObjectString + '.Class.InvokeProperty( "GET", "' + $Property.name + '", ' + $ObjectString + ', $Args )'
    $getScript = $ExecutionContext.InvokeCommand.NewScriptBlock( $instanceScriptText )
    $setScript = $null
    Attach-PSProperty $targetObject $Property.Name $getScript $setScript -override:$Property.override
  }
  $instance
}

function __PSClass-InvokeScript($class, $script, $object, [array]$params) {} # I would love to remove this pointless function, but then I can't repro...

function __PSClass-InvokePropertyMethod($Class, $PropertyType, $PropertyName, $instance, [array]$params) {
  __PSClass-InvokeScript $FoundClass $property.SetScript $instance $params # I would love to remove this pointless function call, but then I can't repro...
}

function Attach-PSNote([PSObject]$object, [string]$name, $value) {
  $member = new-object management.automation.PSNoteProperty $name, $value
  $object.psobject.members.Add($member)
}

function Attach-PSScriptMethod([PSObject]$object, [string]$name, [scriptblock] $script, [switch] $override) {
  $member = New-Object management.automation.PSScriptMethod $name, $script
  $object.psobject.members.Add($member)
}

function Attach-PSProperty([PSObject]$object, [string]$name, [scriptblock] $get, [scriptblock] $set, [switch] $override) {
  $scriptProperty = New-Object management.automation.PsScriptProperty $name, $get
  $object.psobject.properties.add($scriptProperty)
}

$AnimalClass = New-PSClass Animal { property Legs {"None"} }
$Animal = $AnimalClass.New()