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: 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.
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: 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.
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.
Other mistake: When Rey returns to Tatooine to bury Luke and Leia's lightsabers in the sand, it appears that the Millennium Falcon is missing its landing gear, all that is shown on screen is the ramp and its supports, but no rear landing gear. (02:10:03)