Continuity mistake: After the speeder chase, everyone lands in quicksand. In one shot, 3PO is buried headfirst. In the next, he has flipped and his upper body is visible.
Other mistake: When Kylo/Ben leaves the Endor system to go to Exogol, he takes an old Imperial TIE Fighter he supposedly found in the Death Star remains. However, it is established in the previous films that that TIE fighters are short range fighters that are not equipped with a hyperdrive.
Other mistake: Rey pilots Luke's X-wing to Exegol from Ahch-to. However, the door to Luke's hut on Ahch-to was seen in TLJ to be an X-wing wing. It is even referenced as such in The Last Jedi visual guide which specifically states it's a wing from Luke's fighter. No way to fly it if it's missing a wing, and when it's lifted out of the water we see it has all its wings intact.
Other mistake: The Millennium Falcon crash lands on Kef Bir, leaving a long trail of destruction, supposedly because the landing gear is malfunctioning. However, the Falcon has always had vertical takeoff capability, so even if the landing struts were damaged, there would be no reason for this type of crash landing.
Plot hole: While the pair are duelling on Kajimi, Kylo Ren only realises Rey is onboard his ship when the mask of Darth Vader is force-teleported between them. However in this same fight Rey is wielding the dagger, which Kylo must have known was also inside Ren's chambers before the fight. So he should've been able to determine Rey's location earlier.
Other mistake: The remains of the Death Star would not look like that after being blown up and then crashing on to a planet, the remains would be a crumpled mass of metal. The Emperor's throne room was situated on top of a tower which was shown in ROTJ - it would not have survived the destruction or the collision with the planet in the way that we see it.
Factual error: A piece of ship that size crash landing into a planet and not being destroyed would be an extinction level event. The asteroid that supposedly killed the dinosaurs was a lot smaller.
Plot hole: Kylo has to manoeuvre his Tie Interceptor through the space dust around Exoghul yet later on the Rebels/Republic fly hundreds of ships through it. It would take days to fly that many ships through and many of them would not fit through it.
Factual error: After the speeder chase the gang lands on quicksand. Not only do they not sink into it until after the stormtroopers are dealt with, but they suddenly sink at great speed. On top of that quicksand is heavier than air so there is no way that it could have floated and formed the roof of a cave like that. It would simply fall in and sit on the floor, in point of fact it would never have been able to sit like that at all.
Continuity mistake: When the First Order council is gathered, in the wide shot where Kylo Ren says, "We have a spy in our ranks...", he walks behind the council members, and General Pryde is nowhere to be seen. In the next shot, he appears out of nowhere, sitting opposite General Hux and glaring at the latter as Ren walks by him. In fact, in the first shot, a completely different officer is sitting in Pryde's chair, between a man with grey hair and General Quinn, the man that Ren slams into the ceiling. However, when Quinn says, "These allies on Exegol...", Pryde can be seen sitting in the chair instead. The previous occupant is much younger than Pryde and his face has a different shape. Plus after Reb says, "I sense unease about my appearance, General Hux", in the next shot, a completely different woman is sitting next to the man. The first one is an older woman with grey hair, while the second woman is middle-aged, with brown hair. As General Quinn says, "What is it, a gift?", the older woman is back. In addition, when the younger woman appears, the person sitting on her right can be partially seen, and it is a different person than earlier (a Caucasian person, as opposed to the black man that appeared next to the older woman earlier in the scene). (00:20:15)