Definately a defrosting problem probably electronic, re programming required may also be hot gas defrost and evap fan starting too early or running with defrost.

If the equipment has been selected individually and a control panel "custom" built the problem will lie with the panel controller or the way it is wired, I have come across similar panels before with evap fan on with heaters/hot gas valve, compressor and heaters on together, termination stats wound up to the max trying to cure ice up problems.

Are you losing a lot of product or is the product still ok when you probe it, is the temperature display and oblong shaped electronic item or a dial thermometer.

Sounds like you need a more experienced engineer.