I have never in my life heard someone pronounce the 's' in 'est', are you sure this is a thing ? I'd be really curious to know in which instances you heard that, did you hear it in a movie or a footage you could possibly link to ? Honestly I think you were picking up on something else, like the "ce" in "est-ce que ça va ?" I don't know, just a theory

I am almost sure it was meant to be a form of the verb être but you make a good point Raoul, it might have been something that came afterwards. Last time I suppose I heard it, it was on a interview on tf1 but I am on a lookout, or should I say earout, for another instance.