Scratch is lovely, but it should be fed as an extra only. Meat birds or layers, they will need a formulated feed that meets their nutrient requirements. On the "rubber" egg, I wouldn't worry if it's a young layer. Young layers lay a few odd eggs, including soft shelled or shell-less eggs while they work out the kinks in their systems. If it's an older, more experienced layer it could be down to a number of causes, such as inadequate calcium in her diet, stress, internal or external parasites, heat stress or certain diseases. If it's only the occasional egg I wouldn't worry though.