Sometimes when seeds open and fall off the seedling, a little transparent skin is left on seedling. Remove it. I gently spray/mist it with water to loose it and make it softer and gently take it of using tweezers or a toothpick. Take a look at the brown spot at the tip of seedling it will help you see the skin. When you spray it you will maybe slowly see the skin start to crack and open or slide off.