Can you tell me about the story of the Yogi who visited Sai Baba hoping to achieve a spiritual state?

Certainly. Chapter 23 narrates an incident involving a practitioner of Yoga (Yogabhyasi) who came to see Baba with Nanasaheb Chandorkar. This yogi had deeply studied the Yoga Shastras but was unable to achieve Samadhi (intense meditation). He came for Baba's darshan with the specific hope that the "King of Yogis" would bestow grace upon him, remove his doubts, and enable him to achieve Samadhi. However, upon arriving at the Masjid, he was met with the sight of Baba simply eating bread (bhakar) with onions.