Sunni scholarship treats the hadith corpus as pointing to a person not yet born and not yet identifiable, and its weak chains are precisely why a body of modern Sunni scholarship treats belief in the Mahdi as popular expectation rather than a required article of faith, even where it remains widespread devotionally.
Twelver Shia belief draws mainly on a separate, parallel hadith and historical literature specific to the imamate, identifying the Mahdi as a particular historical person, the twelfth Imam, said to have gone into occultation in 874, rather than resting the claim primarily on the Sunni Sunan reports treated here; the two textual traditions overlap only partially; and the Twelver case rests on the doctrine of the imamate rather than on reworking this hadith's chain of transmission.
The Ahmadiyya movement takes the opposite approach to the same Sunni corpus: rather than treating the isnad problems as reason for caution, it reads the hadiths, together with other reports concerning the Mahdi and the return of Jesus, as already fulfilled in one person, Mirza Ghulam Ahmad, who died in 1908 having claimed the office in his own lifetime. That reading of the same texts is the central reason Ahmadis are rejected as Muslims by Sunni and Shia authorities alike, and is legally codified in Pakistan.
Sources Sunan Abi DawudAbu Dawud al-Sijistani with An Introduction to Shi'i Islam: The History and Doctrines of Twelver Shi'ismMoojan Momen, Prophecy Continuous: Aspects of Ahmadi Religious Thought and Its Medieval BackgroundYohanan Friedmann