Sabudana (tapioca pearls) is made from cassava tuber. In Jainism, many followers avoid root vegetables and underground tubers because pulling them up harms many tiny life-forms in the soil and because the whole plant is often destroyed. Sabudana is processed from that root, so it is treated like a root-based food. Different Jain communities (Digambar/Shwetambar) may vary in strictness, but the conventional practice is to avoid sabudana.

You can read more here and about root-vegetable avoidance here .