Answer: It's normal for rubber trees to lose their lower leaves as they grow, but it is not normal for your plant to continue to lose leaves all the time. Plants go through an adjustment period when first moved indoors and they can lose some foliage but after a few weeks they adjust and begin to grow. Since yours is still losing leaves, I suspect the cultural conditions are not quite right for your plant.
Rubber tree plants will grow in low to medium bright light, needs moist but not soggy soils, and responds well to feeding with a half-strength liquid fertilizer every 3-4 weeks. Dropping foliage that otherwise looks healthy usually indicates root rot from overly saturated soils. I'd unpot the plant, then repot it with fresh soil. If you find any mushy roots or a strong odor when you unpot it, it probably is suffering from root rot. Try pruning away any affected roots and repotting in fresh soil.
Hope this helps!
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