What problem did Das Ganu encounter while working on the Ishavasya Upanishad, as mentioned in Chapter 20?

According to Chapter 20, Das Ganu undertook the task of creating a commentary on the Ishavasya Upanishad, titled 'Ishavasya-Bhavartha-Bodhini.' His goal was to explain the meaning of each word from the Sanskrit scripture in simple Prakrit language for those unfamiliar with Sanskrit. While he managed to translate the text word for word, he became troubled because he felt he had not grasped the 'internal secret' or the deep, underlying meaning of the Upanishad. This lack of profound understanding left his mind with 'no joy,' and it was this specific doubt that compelled him to travel to Shirdi to seek the guidance of his Satguru, Sai Baba.