What specific problem did Das Ganu face with the Ishavasya Upanishad, and how did Sai Baba propose to solve it according to Chapter 20?

According to Chapter 20, Das Ganu was composing a commentary titled 'Ishavasya-Bhavartha-Bodhini' to make the Upanishad's meaning accessible. While he successfully created a word-for-word translation, he found that he could not grasp the 'internal secret' or the deeper essence of the scripture, which left his mind without joy. Feeling stuck, he took this doubt to Sai Baba in Shirdi. Instead of giving a direct explanation, Baba told him that the resolution to his specific doubt would be provided by a maidservant at Kaka’s house when he returned there, a unique method of instruction highlighted in this chapter.