I heard Baba sometimes said 'Chal Hat' to his devotees. Could you tell me about Sapatnekar's experience with this?

Yes, the Shri Sai Satcharitra details Sapatnekar's specific experience with this in Chapter 48. Whenever Sapatnekar would go to bow to Sai Baba, he was unerringly met with the rebuke "Chal Hat." This caused him immense pain and confusion, as he saw Baba behaving with "extreme love" towards everyone else. He was tormented by thoughts about his past karma and sins, feeling that his forehead was uniquely marked by this dismissal. This treatment continued until, in a state of desperation and resolve, Sapatnekar approached Baba for a final plea, which led to a miraculous incident that revealed Baba's all-knowing nature and turned Sapatnekar's despair into deep, unwavering faith.