Using 0.5 mm gauge copper is pretty thin (24 gauge) and to expect it to hold up to multiple layers of enamel is likely the problem. Your metal base needs to be thicker along with your counter enamel otherwise you have to put less enamel on the metal, maybe only one thin coat per side.

well, I domed and used two layers of counter enamel on the next one and achieved my objective.. I ended up with a piece with slight doming.. convex not concave .. so I am happy.

Thank you all for your help, it is much appreciated