Why can't I beat Hypothermia?

I cannot beat Hypothermia when I begin a new rimworld. Every(!) game I start, even in the dessert, my colonists immediately suffer from Hypothermia. Group hugging around campfires doesn't work, the hypothermia goes up and up and up. Temperature at this spot is 28°C.

So, what's the trick beating hypothermia early in game, when it doesn't appear random anymore and even kills the settlers standing at a fireplace?

Two of them are wearing Hyperthread winter cloaks, that are supposed to keep them warm and dry Difficulty is level 2, storyteller is Chillax

It seems that you are playing some modded version as Winter Cloak is not an item in vanilla Rimworld.

As you say in your comment, it might be a bug.

To prevent hypothermia in vanilla Rimworld either wall up and use a heat source or use proper winter clothing (parkas, tuques)