Have you been using this metal before? Anything different in the process? Attached is pdf Ivoclar (Maybe it was even Williams) made years ago in reference to metal/porcelain issues.
Fastest way to strip porcelain? Heat the bridge over a bunsen burner and dip it into water... Be careful to not over heat and wear a protective glasses!!!!!
“ keeps fracturing due to porosity or whatever “ Until you figure out the “whatever “ , chances are your 3rd time will probably end up like the last 2.