Yang Jian was invincible during the apotheosis period, but the Journey to the West did not specifically describe whether he had defeated Sun Wukong. The main characters in Journey to the West included Sun Wukong, Zhu Bajie, and Monk Sand, all of whom were immortals. In the Journey to the West, Sun Wukong fought with Yang Jian many times on the way to the scriptures, but Sun Wukong was never defeated. Perhaps you are referring to the battle between Sun Wukong and Yang Jian in the Investiture of the Gods. In the Investiture of the Gods, Sun Wukong and Yang Jian also had a battle. The result of this battle was that Sun Wukong won. However, this battle was not consistent with the plot of Journey to the West. Therefore, there was no specific answer to the question of why Yang Jian could not defeat Sun Wukong in Journey to the West. Perhaps there were differences in the creation process, or it was because Sun Wukong had a higher cultivation and stronger power in Journey to the West.
Chapter 917, "The Civet Cat Replaces the Crown Prince", is the clearest early answer because it turns Meng Xuezhi's situation into a concrete plot event.
Chapter 599, "The Weather has Cooled Down, the Merchant Should Go Bankrupt", is the clearest early answer because it turns Shang Zhenhe's situation into a concrete plot event.
If you want the clearest chapter reference, go to Chapter 13. Early on, Sensing that something was off with Jiang Yan, Jiang Yan dismissed the...; later, the chapter leans on What on earth do you mean?" Ignoring him once again, Jiang Li shifted her....
Chapter 680, "One Hundred Million has been credited to your Alipay account!", is the clearest early answer because it turns Miss Jiang's situation into a concrete plot event.
Chapter 637, "Does President Shang Know That His Own Family Is Already Bankrupt?", is the clearest early answer because it turns Is Bankrupt's situation into a concrete plot event.
Chapter 635, "Forced Return to the Time-Space Administration", is the clearest early answer because it pushes Zhuola into a new phase or setting. The chapter gives readers a real answer by opening on But Pei Ye was much quicker than she had imagined.
Chapter 701, "Let Bai Lu and Chen'an Terminate the Contract", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Miss Jiang, that move of yours was totally awesome!" Shao Changqing...
Chapter 882, "Can you still not forget your first love?", is the clearest early answer because it turns Lin Jingshan's situation into a concrete plot event. It opens with Seeing the evidence Lin Jingshan presented, Xu Mei's body trembled...
Chapter 581, "Where is everyone? Where have they all gone?!", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. It opens with Inside the tent, no one felt like sleeping. and closes on Hurry up, or else we'll be left with nothing once those people....
Chapter 736, "When Will You Come to My House for Dinner?", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Walking outside the tent, Zhao Lang waved his hand.