A quality bar of handmade soap will often "sweat" in humid weather due to the high content of natural humectants. A humectant is a substance that readily absorbs moisture from its surroundings.
Glycerin is a humectant that is a natural byproduct of saponification, the chemical reaction that produces soap. In commercial soaps, the glycerin is removed and used to produce commercial lotions. Handmade soaps, rich in natural glycerin, are the most moisturizing soaps you can find! When you wash with natural soap there is a thin layer of natural glycerin left behind, which will draw moisture to your skin. The general health of the skin relates directly to its moisture content. All natural handmade soaps can help the skin maintain a moisture balance while nourishing the skin.
When natural soap sits out in humid conditions, the glycerin in the soap will draw the moisture out of the air and onto the soap. So the sweating is actually moisture from the air that the glycerin attracts, not moisture coming from inside the soap. The more humid the environment and the more humectants in the soap, the more likely you'll experience this phenomenon.
Honey, for example, is also a natural humectant, attracting and retaining moisture in the skin. Castor bean oil also moisturizes by acting as a humectant. So soaps and shampoos containing added honey, and shampoo bars with loads of castor oil, may sweat even more. There is nothing wrong with your soap, it's just the glycerin and other natural humectants doing their job.
Please understand that when you receive your soaps during humid weather conditions, some of the soaps and wrappers may be damp or wrinkled from the natural "sweat" of the soaps.
There is nothing wrong with your soap and it is not melting, it's just the glycerin and other natural humectants doing their job.