So I'm using the Start Site Workflow web part, and I have one other which has worked fine. No problems there.
My workflow is a site level workflow, I have created a Nintex Start Form from the Workflow Settings, saved it, and re-published it. However, when I go back to my web part page where I want to add it, it's not in my Start Site Workflow dropdown list. It is in the same site as the web part page.