Which of Sai Baba's devotees was involved in an incident with robbers over a bundle of sugar meant for ants?

The devotee you're asking about is Kashiram. According to the narrative in Chapter 0, Kashiram was a cloth seller who, on the advice of a saint named Janakidas Baba, carried powdered sugar to feed ants. Once, while returning from a market, he was attacked by Bhil robbers who mistook his bundle of sugar for treasure. Because this bundle was very dear to him, Kashiram fought the robbers, killing two before being struck unconscious with an axe. He survived the encounter due to his faith in Maharaj.