According to Osho, you feel loose and natural with him because his presence is non-coercive—he offers love and freedom, never forcing anything. The ashram, however, is part of the world: an organization with rules, roles, and necessary discipline. Don’t identify him with the institution; he is a temporary outsider, the ashram a lasting structure. Endure the organization for the sake of the meeting, and don’t be disturbed by it.
You relax with Osho because he doesn’t control you; the ashram is a worldly place with rules, so don’t confuse it with him.