Should Palpatine have been so surprised by Rey and Kylo Ren's Force dyad connection in Star Wars: The Rise of Skywalker? Returning for the divisive final installment of Disney's Star Wars sequel trilogy, Emperor Palpatine was revealed to be the shadowy puppeteer behind the First Order from the very beginning. Following his apparent death in Return of the Jedi, Palpatine's essence was placed into a clone body on Exegol but since this vessel was far from stable, Palpatine orchestrated events by using Supreme Leader Snoke as a glorified ventriloquist's dummy. Palpatine's grand plan was to manipulate his granddaughter Rey into accepting the full legacy of the Sith into herself, thereby becoming Empress Palpatine.
During The Rise of Skywalker's final confrontation on Exegol, Palpatine typically fails to anticipate the strength of will both Rey and Kylo Ren, now redeemed as Ben Solo, possess. As the two Jedi fight back against the mastermind of their misery, their power is revealed to be a dyad in the Force - an extremely rare and extremely powerful link between two Force sensitives. Palpatine is taken aback to see the power of Rey and Ben's Force dyad, and changes his plans on the fly. Instead of transferring the Sith into Rey, the villain decides to simply harvest the power of the dyad to restore his own physical form, ensuring the Sith continue through him.
Palpatine altering his evil plot so quickly suggests that until witnessing Rey and Ben fight together on Exegol, the Emperor had no idea that they were the Force dyad of prophecy. However, Palpatine himself offers useful exposition revealing exactly what a Force dyad is, proving that he did at least have knowledge of the phenomenon, even if he didn't recognize it right in front of him. The actions of Snoke in The Last Jedi also have to be taken into account. Although the bond between Rey and Kylo Ren is first introduced in The Force Awakens, it's Rian Johnson's follow-up that delves headfirst into the concept, and The Last Jedi sees Rey and Kylo Ren regularly make long-distance Force-fueled Zoom calls to each other.
But when Rey and Kylo Ren confront Snoke in the Supreme Leader's throne room, the Palpa-puppet reveals that he knows all about their liaisons and claims to have connected the duo via his own powers. According to The Rise of Skywalker's visual dictionary, the assertion that Snoke was directly responsible for connecting Rey and Kylo Ren was an outright lie, but the scene does at least highlight how Snoke was aware of a special connection, and that he was deliberately encouraging it in order to bring Rey to him. If Snoke had this much knowledge and Palpatine was acting through Snoke, how could the Emperor not have connected the dots and realized Rey and Kyo Ren were a Force dyad?
The real life answer, of course, is due to Rian Johnson and J.J. Abrams having very different visions for the Star Wars sequel trilogy. In The Last Jedi, the Force connection is facilitated by Snoke who is then killed, leaving Kylo Ren as the main villain. The Rise of Skywalker reintroduces Palpatine, makes Snoke a puppet, redeems Kylo Ren and rewrites his Force link to Rey as a naturally occurring phenomenon.
Unfortunately, the inconsistency is far harder to explain in narrative terms. One possibility is that Snoke was semi-independent; that despite being a synthetic being, Snoke could still learn things and make plans without Palpatine dictating every word. If this were true, Snoke might've learned about the connection between Rey and Kylo Ren but not realized its significance, meaning the truth didn't pass on to Palpatine. Secondly, it's possible that Palpatine's hubris made him underestimate the Force dyad until he felt it in person. The power is such a rare one that the Emperor perhaps didn't know it could restore his physical form until getting up close and personal. Palpatine's lack of Force dyad knowledge is one of several examples of poor planning in the Star Wars sequel trilogy and in hindsight, it might've made more sense if exploiting the Force dyad was Palpatine's plan from the start, even though this would've negated the "Rey Palpatine" twist The Rise of Skywalker was so keen to push.