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LTC4000 & LTC3890 and the ITH pin

I have connected LTC4000 with LTC3890 to create a UPS  with a Li-ion battery pack. I have problem that the pin ITH has always the value 0.4V. As a result the voltage out the converter (LTC3890) drops from installed value 21.3 to 16.1V. Also the converter will drops even lower to 12V when i use a current = 4.5A throw it. My problem that its not known why the voltage OF the ITH pin keeps at its maximum value = 0.4V. Thank you in advance. I attached a simulation. (I dont face this problem in the simulation)