After a second look, the original code was setting "value" only once upon initial render when panResponder was initialized with useRef. Since value was, by default, set to 0 - this code was effectively doing the same thing as my fix. This code could have caused bugs in its current state - for example, if the developer mounted the component with a starting value for "value" of a number greater than 0, it could have prevented the index from being incremented since position would never be greater than value. The reason it broke with dynamic children was because "value" was permitted to update whenever the dependency on length was added.

Would it be worthwhile to consider added a minimum dx threshold to change TabViews? Right now, as long as Abs(dx) is greater than Abs(dy), even if it's a very small number, a pan will always initiate the view change. Is that desirable? Or should we be checking if the pan is more than, say, 25% of the screen width?