engine cools down — logbook Toyota Avensis 2001

In the spring I changed the thermostat (as the autopsy found out, the middle part of it fell apart), an external sign was the uneven movement of the temperature arrow. Posted the original. In the summer, the radiator was removed and washed.

As a result, the other day it was -24, a warmed-up car cools down while driving around the city, is this normal?

Previously, this was observed only in frost when the car is standing and idling at -30-35.