I just upgraded to UserForms 0.5 (SS 2.4.7) and after the user clicks Submit, the On Complete message doesn't show (although the form is successfully submitted).
I've tested on localhost and the live site. I even had it not show the On Complete message initially, then after clicking around (not sure exactly what I did), it showed up. But then I couldn't get back to the form page. Even closed the browser and relaunched, then tried opening a different browser, the message was still stuck on the page. After 5 min. or so, I was finally able to view the proper form page again…strange.