Since the lastest patch, when you die and respawn, or just simply joining a server for the first time, your character spawns in with the white underwear and no clothes on. And none of them are visible in the inventory either.

You cannot pick up clother from the ground, to change your look, but can take small items like food/drink/ammo if you have space in the inventory.
After relogging all the clothes become visible again and can be changed as normal.