Temperature are falling quickly these days.
We've fallen from 9 degrees to 2 degrees recently.
Here is a mileage chart of my daily trip at 9 degrees:
Here is the same trip but with 2 degrees ambient temperature:
Lower temperature affects engine temperature: lower values lead to lower efficency and higher consumption.
The HV battery can provide less current, so EV mode can't be used as much as in summer.
Even low speed starts cause the engine to turn on.
Car heating worsens the situation even more, causing the engine to run just to produce hot air.
This can be seen in the ICE statistics:
At 9 degrees, ICE is off 40.1% of the time
At 2 degrees, ICE is off only 36.9% of the time.
By comparison, here is the same trip with hotter weather in November (I wasn't tracking temperature at the time):
Mileage was off the scale at 25.4 km/l (3.9 l/100km), but I've scored even better values in the summer.
ICE was off 60% of the time.