Seeking help with operational issues of the Caddley freezer

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Our company’s utility systems are equipped with a Kaideli refrigerator. The operating condition is set at -10°C. The refrigerator and the buffer tank form an internal circulation system, while the buffer tank and the workshop heat exchanger constitute an external circulation system. No measures have been taken to regulate pressure or flow in the internal circulation system; however, there is a valve that controls the pressure before the fluid enters the buffer tank in the external circulation system. Ethylene glycol is used as the chilled water; the freezing point was measured to be -26°C using a freezing point detector, with a corresponding concentration of 42.2 and a density of 1.059. Recently, the refrigerant has shown unstable heat exchange efficiency, manifested in the following ways: 1) it takes longer to reach the temperature set by the system; 2) the temperature at the compressor’s outlet pipe is sometimes high (indicating good heat exchange and thus less time required) and sometimes at room temperature (indicating poor heat exchange and thus more time required); 3) more frost forms on the outside of the compressor compared to before; 4) the sight glass for the compressor’s refrigeration oil sometimes contains many bubbles and other times the liquid inside is relatively pure. The manufacturer now wants to determine separately what the temperature is when the chilled water reaches freezing point ； It is suspected that there are deposits or crystals on the outer wall of the heat exchange tube between the refrigerant and the chilled water. May I ask where the problem lies? What should a better solution look like? Thank you so much!