I'm not familiar with the thermostats and elements on a State tank or any modern tank for that matter, but some thoughts...
Are you measuring the temperature at the tap and seeing a higher temp than what the thermostats are set to? Any chance you are having a pressure differential problem that is changing the mix ratio?
Do the thermostats switch both sides of the 220V line? Have you tested between the element leads and ground? If the element has an alternate path to ground and the thermostat doesn't switch both sides, some current can flow and might continue to heat the water.
It could be that the thermostat sticks and by the time you get a meter on it could have opened.