Abdul Baha warned young Shoghi Effendi against drinking coffee in the homes of any of the Baha'is.

From his early years, Shoghi Effendi was introduced to the world of suffering and danger which his grandfather had inherited as the Centre of Bahá'u'lláh's Covenant...., the treachery of the Covenant-breakers in the Holy Land reached a point where the Master felt compelled to warn his young grandson against drinking coffee in the homes of any of the Bahá'ís in the fear that he would be poisoned. At the age of fifteen, however, Shoghi Effendi was forced to drink from the bitter cup of sorrow which the machinations of Covenant-breakers would continue to fill for the rest of his life.

(The Life of Shoghi Effendi by Helen Danesh, John Danesh, Amelia Danesh published in Studying the Writings of Shoghi Effendi ed. M. Bergsmo - Oxford: George Ronald, 1991)

https://bahai-library.com/danesh_life_shoghi_effendi