Mostly likely, you accidentally enabled your VizAlert schedules. That would cause Tableau Server to treat it as a typical subscription schedule, while at the same time, VizAlerts would start ignoring it. So the result would be exactly what you are getting--a standard Subscription, with just the image of the viz embedded in the email body. Disable your VizAlerts schedules again, and you should be golden once more.
That was exactly the issue. Thank you for your quick response and knowledge.