1. join this world https://vrchat.com/home/world/wrld_f3fecd46-5697-4e68-8b6f-e938fd8f95ca
  2. Notice that the ambient occlusion is visible through walls (see screenshot)
  3. Switch back to the live version
  4. Issue disappears
I contacted the creator of that world, it seems like the creator used the Mochie Standard shader.