Falling reported thermocouple temperature in warmer room

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I moved ANENG Bluetooth multimeter AN9002 with connected thermocouple from the fridge with 45 degrees F to the warm room with 78.7 degrees F.

Ideally there would be a very fast reported temperature change to 78.7F, and after that reported temperature would remain approximately constant.

To get the real reported temperature as a function of time I used a remote Bluetooth connection from AN9002 to a laptop. The plot of captured 10000 temperature values for about one hour duration is shown on the attached ThermocoupleTemperature.png.

We see that after a fast increase from 45F to 77F the reported temperature drops. Even more interesting, about 2000 seconds later, the reported temperature has a peak, then drops again, finally rising at the end of the hour.

Such strange behavior is a result of not so perfect Cold Junction Compensation.

The internal AN9002 temperature, which is supposed to be used for such compensation, changes slowly. To remove noise, it was filtered by a running average with the size of 60 samples. The result is shown on the attached  InternalTemperature.png.