The issues with the Star Wars sequels remains prevalent.
While some may argue that the sequels are among Star Wars' worst movies, they do have their merits. ittedly, though, there were a number of plot holes throughout Star Wars' sequel trilogy movies. Of all the plot holes across the three movies, big and small, these 10 are the most significant.

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10 The New Republic Never Detected Starkiller Base
Star Wars: The Force Awakens
It was odd enough that the Rebels took quite some time to discover the Death Star, as construction seemed to begin as early as the end of Star Wars: Episode III - Revenge of the Sith. This made the New Republic being unaware of Starkiller Base all the stranger. In fact, in The Force Awakens, the joke is explicitly that Starkiller Base is like the Death Star but much bigger.
Yet, the attack on the New Republic appears to come from out of nowhere, at least from the perspective of the Resistance, and they seem shocked when Starkiller Base is revealed to them. Unlike with the discovery of the Death Star, though, which has been set up in Andor and will no doubt continue to be explored in the Andor season 2, the sequel trilogy offered no explanation for why Starkiller Base went undetected. Particularly given its size, this is a significant plot hole in The Force Awakens.
9 Luke's 'Unfindable' Island Had Massive Significance To The Jedi
Star Wars: The Last Jedi
Luke Skywalker's sequel trilogy arc was generally unfavorable among viewers, particularly because it seemed like such a deviation from his character throughout the original Star Wars trilogy, Return of the Jedi in particular. One of the most significant aspects of this change was Luke's abandonment of the galaxy and decision to exile himself to Ahch-To after his nephew, Ben Solo, had fallen to the dark side of the Force and become Kylo Ren. However, the choice of Ahch-To was rather odd.
Why would Luke choose the very birthplace of the Jedi as his hiding place?
In Star Wars: The Last Jedi, Luke described Ahch-To as "the most unfindable place in the galaxy." However, Ahch-To actually had an immense significance in the Star Wars galaxy, especially for the Jedi. Specifically, Ahch-To was the location of the very first Jedi Temple. This begs the serious question: why would Luke choose the very birthplace of the Jedi as his hiding place? This seems like a major misstep, enough so that it reflects a major plot hole in The Last Jedi.
8 Leia Was Able To Fly Through Space
Star Wars: The Last Jedi
One of the single most controversial moments in the entire sequel trilogy came when Leia Organa was shot out into space from an attack on her ship but then managed to fly back to safety. This moment went beyond an incredible Force feat—even Anakin Skywalker, the Chosen One himself, could not have accomplished such a thing. In fact, Star Wars hadn't even directly confirmed Leia's Force abilities prior to this moment, making it even more bewildering at the time.
Even with Leia's Force-sensitivity now clearly canonized, though, Leia flying through space via the Force and living to tell the tale remains a massive sequel trilogy plot hole. It remains unclear how even the Force could have enabled Leia to survive in space with no protective gear, including a helmet, and then fly back to her ship using nothing but her body. Hopefully, Star Wars will not repeat this odd ability, but it would do well to explain it in some way and address this plot hole.
7 Anakin's Lightsaber Was Ripped Apart...Then Suddenly Fixed
Star Wars: The Last Jedi
Anakin Skywalker's blue lightsaber is one of the single most iconic objects in all of Star Wars. First introduced in A New Hope when Luke was given his father's old lightsaber by Obi-Wan Kenobi, the weapon returned in the prequel trilogy (as Anakin's lightsaber, naturally) and then appeared yet again in the Star Wars sequels when Rey shockingly discovered it at Maz Kanata's castle in The Force Awakens. However, the lightsaber seemed to meet a tragic end in The Last Jedi when Rey and Kylo Ren tore it apart while fighting over it.
Yet, Anakin's lightsaber was remarkably fixed without explanation in Star Wars: The Rise of Skywalker. This was unfortunately a common issue in The Rise of Skywalker, which also saw the return of Kylo Ren's formerly destroyed mask with minimal explanation. In fact, this was a symptom of a much larger issue in the sequel trilogy, wherein each addition to the trilogy seemed to actively undo what had come before.
6 Leia Had The Force But Didn't Use It On Crait—Including To Lift Rocks
Star Wars: The Last Jedi
As mentioned, the Star Wars sequels finally confirmed what the original trilogy had only hinted at: Leia Organa did have the Force. However, she was very minimally seen using it on-screen, and The Last Jedi even seemed to forget that Leia had such incredible power in the Force that she was able to fly through space. Specifically, at the end of The Last Jedi, the Resistance fighters found themselves trapped in a cave on Crait. Ultimately, Rey saved the day by lifting rocks to clear a path for them.
The plot hole here is that Leia never even tried to lift the rocks herself, despite evidently being incredibly powerful in the Force. This is quite odd, particularly given how dire the situation was. The Resistance was as close to being extinguished as they'd ever been, yet Leia acted nearly helpless throughout this entire battle.
5 Lightspeed Skipping Breaks All The Rules Of Hyperspace
Star Wars: The Rise Of Skywalker
The Rise of Skywalker very controversially introduced the notion of 'lightspeed skipping,' which, as the name suggests, is the ability to jump to lightspeed multiple times in quick succession. However, the concept of lightspeed skipping completely broke with Star Wars canon. Until The Rise of Skywalker, it was well-established that ships couldn't jump to hyperspace until they had left the gravitational field of a planet.
Yet again, this unfortunately went minimally explained in The Rise of Skywalker. In fact, this is one of several examples from The Rise of Skywalker of a concept that 'broke the rules' of Star Wars but was left without explanation within the movie itself. While Star Wars books and comics have done some work to flesh out this and other plot holes in The Rise of Skywalker, it nevertheless represents a major sequel trilogy plot hole.

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4 "They Fly Now" Suggests Stormtroopers Didn't Fly Before—But They Did
Star Wars: The Rise Of Skywalker
The sequel trilogy is full of lines that have been heavily criticized (and turned into memes), but one of the most significant is the chorus of "They fly now?" between C-3PO, Finn, and Poe Dameron in The Rise of Skywalker. With this line, all three characters were expressing disbelief that, evidently, the stormtroopers had just recently gained the ability to fly. However, that is far from the case; stormtroopers had the ability to fly in Star Wars long before The Rise of Skywalker.
In fact, the very origins of the stormtroopers, the clone troopers, had already been equipped with jet packs. Clearly, in light of this history, the idea of flying stormtroopers was not all that revolutionary. Indeed, even the Empire's stormtroopers were at times equipped with jet packs, as shown in Star Wars Rebels. Moreover, while Star Wars might have been able to argue that Finn and Poe simply hadn't seen that before, C-3PO's involvement in the conversation spoiled that. Given his longstanding history in Star Wars, C-3PO absolutely would have known that stormtroopers could fly.
3 C-3PO Knows The Sith Language
Star Wars: The Rise Of Skywalker
Truthfully, The Rise of Skywalker was full of plot points that felt rushed and loosely explained, one of them being C-3PO's programming including the Sith language. While C-3PO was an immensely capable protocol droid, it makes little to no sense that he would have access to the Sith language. After all, a very young Anakin Skywalker had built C-3PO and while, ironically, that same maker had gone on to become a Sith himself, he would not have even known to program C-3PO with that language, nor, presumably, would anyone else.
Where and how C-3PO acquired this language remains unexplained in the franchise, but it's quite clear that he did. In fact, it became absolutely pivotal that C-3PO was able to translate the Sith language, as this was how the heroes obtained another Wayfinder. Sadly, though, this became yet another example of a massive plot hole in The Rise of Skywalker.
2 The Resistance Went From Having No ers To A Fleet Of ers
Star Wars: The Rise Of Skywalker
In The Last Jedi, the situation became incredibly dire for the Resistance. On Crait, they were backed into a corner by the First Order, and they seemed to be on the brink of extinction. In fact, the Resistance called for help, and no one came, even when their distress signal made it clear that this could be the end of the Resistance entirely. It was only because of Luke Skywalker's trick on Kylo Ren and Rey's arrival with the Millennium Falcon that the Resistance survived at all.
The Rise of Skywalker completely rewrote this by revealing that, evidently, a massive fleet of fighters was ready to the Resistance.
However, The Rise of Skywalker completely rewrote this by revealing that, evidently, a massive fleet of fighters was ready to the Resistance. It's unclear what would have made such a massive difference between The Last Jedi and The Rise of Skywalker, particularly because the Resistance also seemed to be on the brink of complete destruction in The Last Jedi; the urgency should have therefore existed in that situation, too. Unfortunately, this remained a plot hole, with only Lando Calrissian's ability to find being used to explain this major shift.
1 Somehow, Palpatine Returned
Star Wars: The Rise Of Skywalker
Easily the most heavily criticized and best-known sequel trilogy plot hole was the return of Palpatine. After the first two sequel movies had built up Kylo Ren as this trilogy's 'big bad,' The Rise of Skywalker made a shockingly sudden turn, bringing back the villain from the prequel and original trilogies at the last minute. This proved to be a very unpopular move, and it remains one of the biggest sticking points in the franchise.
Star Wars has done considerable work to explain this in canon books and TV shows that have been released since The Rise of Skywalker, but in the movie itself, this remained a massive plot hole. In fact, even now, Star Wars hasn't truly done enough to make this very sharp turn make sense. Ultimately, of all the plot holes in the Star Wars sequel trilogy, this remains the most significant.