Window only visible when attached to parent window

I'm trying to display a window which works perfectly fine when I provide a parent window but if I try to add it to the root layout it's invisble.

Code:

if (g_WndMng.m_pCustomWindow!= NULL)
	{
		SAFE_DELETE(g_WndMng.m_pCustomWindow);
	}
	g_WndMng.m_pCustomWindow= new CWndCustomWindow();
	g_WndMng.m_pCustomWindow->Initialize(&g_WndMng);

Code:

BOOL CWndCustomWindow::Initialize(CWndBase* pWndParent, DWORD)
{
	return InitDialog(g_Neuz.GetSafeHwnd(), APP_CUSTOM_WINDOW, 0, 0, pWndParent);
}

I've used this code successfully countless times to display other windows , am I missing something out this time ?

EDIT: //
I'm an idiot, I've moved the window out of sight in OnInitialUpdate() , everything works as expected now. Thanks Kia for slapping me in the face because I am blind lmao.