Another reason I find this interesting is that Torquatus clearly says exactly what Don is saying -- that Epicurus finds the highest good to be in pleasure. That seems clear and does make sense and Cicero does not object on that point.
But Torquatus does not seem to be as clear and successful in explaining Chrysippus' hand or the equation of pleasure as the absence of pain in a way that Cicero finds persuasive. (And I think most of us agree that for some reason - Cicero with his finger on the scale? - the point is not being made clearly.)
But whatever the reason, the "failure to communicate" seems to revolve around this very issue -- clarity and agreement in identifying simply "living, existing, being alive" as being pleasure.