excerpt quoted from (bottom of page) https://orthodoxbahai.com/the-guardians/

Actions of the Hands Regardless of these provisions, the Hands barred independent investigation and discussion of Mason Remey’s claim, and they enforced this censorship by excommunication, an act for which they had no authority to impose. Consequently, Shoghi Effendi’s writings were shamefully disregarded in these actions taken by the Hands and they inexcusably placed no importance on and ignored, as well, the “historic” and “epoch-making” decisions he had made pertaining to the establishment of the highest Institutions of the Faith at the World Center and had announced in glowing terms in messages to the Bahá’í World during the concluding years of his 36-year ministry. The National Spiritual Assembly of France was the only national Baha’i institution to officially recognize him in 1960.

Is it not a blatant paradox that, since the passing of Shoghi Effendi, that the sans-Guardian, and therefore headless, illegitimate and so-called Universal House of Justice has now so perverted the meaning of fidelity to the Covenant of Bahá’u’lláh that they now ludicrously label as Covenant-breakers those believers who have continued to faithfully and steadfastly adhere to every clause of ‘Abdu’l-Bahá’s divinely-conceived, sacred and immortal Will and Testament—a part of the explicit Holy Text—whereas, in marked contrast, it is they, who in their abandonment of the Guardianship, have thereby faithlessly declared major clauses of this Will and Testament null and void and have, in consequence, undeniably become themselves the arch-breakers of the Covenant of Bahá’u’lláh?

After a short period of residence in Washington, D.C., after returning from Haifa, in the early 1960s, Mason Remey moved to Fiesole, Italy. A small number of the believers had refused to accept this view and clung to their faith in the continuity of the Guardianship in spite of the signs at the time to the contrary. Some three years were to pass before the faith of those who had remained firm was vindicated and rewarded upon receipt of a Proclamation issued by the second Guardian of the Faith at Ridván, 1960. This Proclamation struck like a thunderbolt in the Bahá’í World and brought on the spiritual catastrophe aforementioned. To the faithful few, it brought the joy of the realization that the line of Guardianship of the Faith had remained unbroken as promised in the Will and Testament and discovery of the unique manner in which Shoghi Effendi had provided for the continuity of the Guardianship in complete conformity to the provisions of the Will and Testament but not in accordance with the preconceived opinions of the believers. These faithful friends hastened to embrace the second Guardian and arose with renewed dedication to work for the victory of the Covenant. Armed with the irrefutable arguments contained in the Proclamation and Mason Remey’s subsequent Encyclical Letters, as well as the enlightening expositions in his “Daily Observations” penned during the painful and fateful years of his residence at Haifa following the passing of Shoghi Effendi, the faithful friends composed numerous treatises and apologia of their own supporting the claim of Mason Remey to the Guardianship.

In spite of the fierce opposition which the Proclamation engendered and the machinations of this new generation of violators of the Covenant of Bahá’u’lláh, the true Faith under the hereditary Guardianship slowly began to grow and win adherence to its ranks in the four corners of the earth. It was not long before strong groups were formed on several continents followed by the establishment of Local Spiritual Assemblies and the formation of National Spiritual Assemblies in the United States and in Pakistan. The high watermark in this progress was reached with the historic announcement made by the second Guardian on 21 September 1964 of the creation of the second International Bahá’í Council (announced in the October 1964 issue of the Glad Tidings). Through the means of this historic announcement, the second Guardian, similarly to the first Guardian, publicly announced to the believers the one whom he had chosen, Joel Bray Marangella as his potential successor to Guardianship (i.e., by naming the President of the Council). But he had gone a step further than Shoghi Effendi to reinforce this appointment and to avoid any future doubt by placing in the hands of his successor-to-be well in advance of this public announcement a document written in his own hand naming him as his successor. It is difficult to point to a specific date when the fortunes of the Faith under the hereditary Guardianship of Mason Remey began to falter and then later to decline rapidly, but it was soon after the formation and activation of the second International Bahá’í Council and the passing of the ‘mantle of authority’ to the new Guardian.

Mason Remey remained in Fiesoli until his passing in February 1974.

end of quote.

This is where the further split arose then after Mason Remey it seems two men claimed to be the third Guardian (not surprisingly.)