Why was Argentina's last-gasp try against England disallowed?

England defeated Argentina 31-24 in a Nations Championship rugby match at the Estadio Unico Madre de Ciudades in Santiago del Estero on Saturday night. A last-gasp try by Clermont wing Bautista Delguy in the right corner, which would have set up a potential match-tying conversion to level the score at 31-31, was ruled out following a lengthy TMO review involving referee Angus Gardner and Television Match Official Brett Cronan. The decision sparked huge controversy among the Pumas, who believed Delguy had grounded the ball successfully despite defensive efforts from Noah Caluori and Henry Slade.