Indeed it was probably insect damage. Most likely it was spider mites as they make tiny webs, usually in the crevices between leaves and stems. But China Doll is also susceptible to mealybug which looks like tufts of cotton. Scale is another serious pest. When you say you cleaned the plant, I assume you meant you washed it off. That may not have been enough to destroy all of the eggs as there are usually several generations of the pests. Consider purchasing an Insecticidal soap for use on indoor plants available at most garden centers. Follow the directions. Watch the plants closely for signs of any of the insects. Spider mites are microscopic but mealybug and scale can be seen. Washing the plant in a shower once a month is a good way to clean the plant of dust and keep it healthy. Keep the soil moist - they will drop leaves if the soil gets too dry. Bright light is essential as well and it seems you are providing that.
