Why did Imam Ahmad ibn Hanbal deny some of Hamza’s recitations, even though they are among the recitations of the seven reciters? Does this indicate that they are not mutawatir (concurrently transmitted)?

Many verifiers have agreed on the widespread transmission (tawatur) of the seven qira'at (readings). If their widespread transmission from the Prophet, peace and blessings be upon him, is established, then no one's denial of them holds any weight. It has not been proven that Imam Ahmad denied Hamza's reading. Rather, it is narrated from him that he disliked reciting with it due to the abundance of assimilation (idgham) and the length of the prolongation (madd). It is also narrated from him that he did not dislike it. Furthermore, some readings may be unknown to a scholar, as happened to Umar ibn al-Khattab, may Allah be pleased with him.