Manual shifter does not work below 45 degrees

The manual shifter works perfectly when the outside temperature is above 45 degrees. However, when the temperature drops below 45 degrees, the manual shifter does not work.

When trying to downshift manually below 45 degrees, nothing happens. The shifter light does not change to a number. It continues to show in position 'D'.

At higher temperatures, all works fine.

This causes a problem when driving down steep hills while not being able to engine brake.

Could there be a rubber somewhere which gets too tight at low temperatures?

Thanks for any help.