Abnormal temperature in the second feed gas heat exchanger of the liquid nitrogen quench tank

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The liquid nitrogen washing system in our company is a Zhongtai Technology cryogenic tank. Recently, the temperature at the hot side of the second feed gas heat exchanger has dropped abnormally, from -100°C to -135°C. As a result, the temperature of the nitrogen used for washing in the nitrogen washing tower, as well as that of the feed gas, increased slightly. Adjustments made through the fuel gas pipeline were ineffective, indicating that the second feed gas heat exchanger was no longer functioning properly; the cooling capacity could not be utilized to cool the nitrogen and feed gas inside the cryogenic tank, nor could it be transferred to the syngas exiting the heat exchanger. Adjustments to the flow rates of the raw nitrogen and the washing nitrogen also proved ineffective. Finally, by rapidly increasing the amount of nitrogen used for washing, we raised the temperature of the feed gas entering the washing tower to -171°C, at which point the temperature trend reversed: the temperature at the hot side of the second feed gas heat exchanger rose rapidly, while the temperatures of both the feed gas and the washing nitrogen decreased rapidly, returning to normal levels. However, the operating conditions cannot be maintained; the temperature at the hot side of the second feed gas heat exchanger will continue to decline. Overall, there are issues with the heat exchange performance of the second feed gas heat exchanger, while no significant changes occurred in the various parameters of the cold box during this period. I was wondering if anyone else has encountered a similar situation?