Seed: 5450957878814971038
How to reproduce?
1 Install 21w42a
2. Open Minecraft
3. Create a New World
4. Enable Cheats
5. Teleport to this coordinates -> /tp @p -4869.513 149 -75.772
6. Go to a block of snow
7. Compare going in the block of snow having no leather armor, having one leather armor, and having a full set of leather armor. 

Then read:

There is a problem with the Freezing damage in the latest snapshot. When wearing only one leather armor, the damage is nullified the same way as wearing a full set of leather armor. It does not slow the freezing damage as it is supposed to do when only wearing minimal leather armor and that's the bug. Maybe the timer is set to minutes rather than seconds? If so, it will be better if it was in seconds since the way it is configured now totally ignore the mechanics. 

Minecraft Wiki reference:

• Entities in powder snow slowly freeze.
  • Once frozen, damage is slowly dealt to the entity.
  • Wearing leather armor is intended to slow the freeze effect, and a full set of leather armor is intended to stop the freeze effect. However, this feature was not implemented properly.