The water cooler for liquefied gas after the catalytic cracking stabilizer cannot be cooled down

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Could everyone help analyze this: The control of the catalytic stabilizer tower is a critical aspect; there is no thermal bypass. After the pressure control valve, there are air coolers and water coolers, all of which are located above the reflux tank. The temperature at the top of the tower is 66°C; after air cooling, the temperature drops to 47°C, and after water cooling it drops to 46°C. The pressure in the stabilizer tower is currently controlled at around 1.1 MPa, while the pressure in the reflux tank is slightly over 0.9 MPa. The air-cooled temperature is okay, but why can the water-cooled version only cool by one degree? Last year, new heat exchanger cores were installed; they are arranged in a 2+2 series-parallel configuration. The water flow rate in one set of tubes is 0.4 m/s, while it is 1.1 m/s in the other set. Even if only one set of heat exchangers is in operation, it shouldn’t be possible to achieve a cooling effect of just one degree. The capacity is 240 t/h of liquefied gas; each heat exchanger has a length of 1 meter and a heat exchange area of 328 square meters. Could all the experts please help analyze this?