When testing WooCommmerce shipping plugins, remember this one thing: It caches shipping results based on your current cart, so to force it to update the results you have to change the cart. The easiest way to do that is to do your test, then increment a product qty in the cart by 1, then test again ( don't reuse a former qty, always increase qty to something never used previously for the current session ), -- repeat.
This might have changed at some point, but if I remember right it caches shipping results, so you have to break the cache by changing the cart for testing purposes.