Wu Zhu's memories had been erased by the Temple. In the novel " Joy of Life," Wu Zhu was a robot. After his memories were wiped away by the Temple, he was even assigned the task of assassinating Fan Xian. Although Wu Zhu had forgotten Fan Xian, out of instinct, he ultimately did not execute the order to kill Fan Xian. After interacting with Ye Qingmei and Fan Xian, Wu Zhu gradually formed his own thoughts and feelings. Although he had lost his memories, he still protected Fan Xian and, in the end, killed the Qing Emperor with Fan Xian. In short, Wu Zhu lost his memory because the Temple had erased his memories.

Wu Zhu's memories had been erased by the Temple. In the " Joy of Life," Wu Zhu's memories had been partially erased by the Temple. He had even been assigned the task of assassinating Fan Xian. Although Wu Zhu had forgotten many things, he had not forgotten Ye Qingmei. While Wu Zhu and Ye Qingmei were together, he gradually gained a human soul. Although a part of his memory had been erased, he still retained his feelings for Ye Qingmei. The specific memory recovery process was not mentioned in the search results provided.
The reason Wu Zhu lost his memory was due to the battle with the Temple Envoy and the influence of external factors. In the battle, Wu Zhu's memory was damaged and he forgot everything related to the temple. In addition, a portion of his memories had been erased by the Temple and he had been assigned the mission of assassinating Fan Xian. Although he had lost his memories, Wu Zhu still had the instinct to protect Fan Xian and Ye Qingmei's descendants. He did not carry out the mission of killing Fan Xian. There was no specific information on how his memory was restored. Therefore, the exact details of Wu Zhu's memory loss were still unclear.
The reason why Wu Zhu lost his memory was because he had suffered memory damage during the battle with the Temple Envoy, and he had forgotten all memories related to the Temple. In addition, he had been assigned the mission of assassinating Fan Xian by the Temple. This had also caused him to lose a portion of his memories. However, Wu Zhu had recovered his memories through Fan Xian's warm awakening. In the novel " Joy of Life," Fan Xian and Wu Zhu met in the temple. Wu Zhu was defined as an intruder who tried to kill Fan Xian. Fan Xian's interaction with Wu Zhu gradually restored Wu Zhu's memories. Finally, he recuperated on Dong Mountain. Thus, Wu Zhu had recovered his memories through Fan Xian's warm awakening.
The reason for Wu Zhu's amnesia was that he had been injured in the battle with the Temple Envoy, causing his memory to be damaged and forgetting all memories related to the Temple. In addition, he had been assigned the mission of assassinating Fan Xian by the Temple. This had also caused him to lose a portion of his memories. Even though he had lost his memory, Wu Zhu still protected Ye Qingmei's descendants, regarding their safety as his instinct. Wu Zhu's identity was the guardian of the temple, and he was also an intelligent robot in the military museum that was built before the nuclear explosion on Earth. As the most powerful and intelligent robot in the temple, he had always been guarding the safety of the temple. Although he had lost his memory, Wu Zhu ultimately did not execute the order to kill Fan Xian. This showed that he had developed human feelings. Thus, Wu Zhu lost his memory because the Temple had erased all his memories.