Is it happening on all the shelves?
Also how old is it and how long has it been installed for?
Ok thats fine.
If the shelves are collecting water and theres nothing touching the back wall inside the fridge then its possibley either the thermostat is faulty ie getting to cold in there as this can cause condensation to form on the glass or the door isnt sealing with warm air entering the fridge and again condensation forming on the glass shelves.
So first check the door seal and check the door is closing ok and theres no gaps in the seal. This can be hard on a built in appliance as depending on were its installed you may not be able to see the seal when the door is closed.
But if the door is closing ok and the seal is fine then its possibley the control thermostat at fault getting to too cold in there. Now this is a control board rather then a thermostat so for this the control board will need to be replaced and hopefully that should sort it out and stopp thick pieces of ice forming on the back wall and the shelves getting condensation forming on it.
Do you have a thermonitor you can place in there to see what the correct temperure is?
As something is causing the condensation to form in there so as the door and seal are fine, theres nothing touching the back wall then its usually getting to cold in there.
No worries, Just let me know what you find.
As the thermostat can be switcing on and off but it could be doing it at the wrong temperture instead.