If we start with the assumption that an ingredient changed upon moving to China, the suspects are:
Flour - It look like Chinese flour has some different terminology. "Regular flour" is low gluten and rather crude. "Standard flour" is the general equivalent of all-purpose flour. There are a number of others of both high and low glutens. Gluten content approximating that of western all-purpose flour is required for the standard western toll house cookie recipe.
(Some flour makers were caught using pulverized lime in bleaching, which, aside from being inedible, alters the pH. But it's unlikely you would encounter that consistently over years.)
Baking Soda - I don't see any reason to think Chinese baking soda is different. It's kind of a secret ingredient in stir fry meat dishes. Old baking soda could be at fault, but, again, 14 years of old baking soda? Are you perhaps finding U.S. or U.K. brands that have been on the shelf in Taiwan for too long? If that's a possibility, ask an apothecary for bicarbonate of soda. I really immediately suspect old baking soda when things fall flat. You can test baking soda by putting a small amount in some vinegar. It should immediately start bubbling vigorously. If it doesn't, it's bad. Toll house batters are, I would say, borderline acidic for baking soda, so it can't stand old baking soda or anything too alkaline in the ingredients.
Baking powder - Some toll house recipes use baking powder or both baking powder and baking soda. Baking powder is even more subject to aging than baking soda, which is pretty stable. Test baking powder by adding a bit to hot water. Baking powder includes its own acid, so if it's good, it will bubble when water activates it.
Chocolate - One thing to check. Dutch process cocoa and chocolate is neutral, and baking soda depends on acidity. "Tollhouse" cookies don't normally have chocolate in the batter, aside from the chocolate chips, but if your recipe does, the difference between neutral Dutch cocoa and regular cocoa could block the baking soda.
I don't think there's much else among the ingredients. A unusually alkaline ingredient can block the baking soda's action. That's why I wondered about the limed flour until I saw how may years were involved.
So check the two most obvious, low gluten or mislabeled flour - and known fresh baking soda.