Why did Sai Baba break his promise to Dev and fail to show up at the Udyapan ceremony in Mumbai? It seems he deceived his devotee.

Contrary to initial appearances, Sai Baba did not break his promise to Dev. As explained in Chapter 40, Baba attended the Udyapan ceremony in the guise of a Sanyasi. He had promised Dev, 'I am coming,' and intended to fulfill his word. When Dev later complained to Jog about being deceived, Baba himself clarified the matter. He explained, 'I said I would come with two others, and I went with two others.' The Sanyasi who arrived with two companions for the meal was indeed Baba himself, though a 'veil of Maya' prevented Dev from recognizing him at the time.