Similar issue occured for my character today.
I was crouched by a fire to dry wet clothing. Managed to raise body temp to 35C (checked with worn Medical thermometer). When I had no status effects besides healty, energized and hydrated I went out in the rain again.
After some running and looting I got the Hypothermia status with no prior warnings besides beeing wet/soaked.
Sitting by a fire did not cure it and my character soon died.
game version 0.58129488