Continuity mistake: Look at the overhead shot of the limo approaching the Presidential palace. The gates including the sandbags where military men are stationed are in the shade. We see then a valet open the door for Margot Robbie, and the spot is in the sun. (00:41:35)
Continuity mistake: When the valet tells Harley that the president wants to see her, the guard behind Harley is looking towards her. For her response, he's facing away from her, and her facial expression is different as well. (00:42:00)
Continuity mistake: El Presidente Luna stops moving and bleeds from his mouth with his palm against the floor. He's wide-eyed dead and motionless, but next time we see him after Harley stops musing over how well-endowed he was, his hand is turned around, palm up. (00:48:35)
Continuity mistake: Ratcatcher 2 tries on some round glasses holding the box with her thumb on the top of the side, into the opening. Wider shots have her hand placed towards the bottom. (00:53:35)
Continuity mistake: The Corto Maltese Army is storming the pleasure district. As the camera pans from the club doors to the incoming vehicles, to the far left there's a john wearing a brown suit posing one-handed in front of a girl. In the wide shot from behind the trucks, you can see that a soldier pushes the guy back to the wall. But as their commander gets off the hum-vee and yells to search everywhere, the guy is standing in the corner, and at the next cut he's back against the wall. (01:01:45)
Continuity mistake: The government forces are rounding up the foreigners outside the bar. Bloodsport finishes his beer and puts it down; the bottle is facing opposite directions in the two shots, just look at the label. (01:02:10)
Continuity mistake: At the beginning of her escape, Harley faces three guards. The rightmost one is smoking a cigarette, then has no cigarette in his mouth, then he has it again. (01:11:25)
Continuity mistake: After killing the guards all around her, Harley rushes into the next room, kicking the door open, and begins fighting in close quarters with more. She breaks the arm of one of the guards who tries to stab her through the bars. In the sequence, the red wrap is covering her fingers in one shot, it's underneath them in the next. (01:12:15)
Other mistake: Escaping from her captivity Harley kills a dozen people with the javelin in brutal gory ways, but when she gets on the taxi the weapon's golden finiments appear to be spotless. (01:14:00)
Continuity mistake: When Peacemaker sticks the detonator inside the explosive after the humorous argument with King Shark, the detonator is suddenly lower in the last shot. (01:21:45)
Continuity mistake: An personal assistant brings news about the attack on Jotunheim. Suarez turns towards her holding a sheet, but in the previous shot he already threw the document on the desk striking a pensive pose. (01:22:05)
Continuity mistake: Seeing all the Starro drones being held captive in the "Dirty Little Secrets" section, Rick Flag says "Good God". Thinker replies "If God existed..." etc. During this sentence Flag lowers the gun slightly before the first cut, but the gun is angled higher as it cuts to Peter Capaldi and even higher in the wider shot. (01:23:05)
Continuity mistake: When Peacemaker kills Rick Flag by stabbing him in the heart, the depth of the object changes between the close-up shot of Peacemaker's hand and the next shot, where we can see the part sticking out of Flag's chest has increased. This is before Peacemaker hits the object deeper. (01:31:05)
Continuity mistake: When Flag collapses after his fight with Peacemaker, his hand is off the shower tray. Peacemaker then talks to Ratcatcher 2, and Flag's hand is well on the tray. (01:31:40 - 01:32:05)
Continuity mistake: When Amanda Waller orders the blonde subordinate to "Open it", the digital clocks show the same times shown minutes earlier when they had yet to wake up, contact them, talk to them, order them to retreat, witness their change of mind. All of which certainly took longer than a minute. (01:46:45 - 01:49:35)
Continuity mistake: When the people in the control room wake up and find out there's "A freakin' Kaiju", the clocks are showing entirely different timezones from the previous instances, with a wild difference from one another (earlier they were a couple hours apart, now we have even 9 hours), and none of which matching the time when the action supposedly takes place (it was late morning, past 10 AM as shown by the surveillance room clock and the phone in the hands of Harley's torturer). (01:46:45)
Continuity mistake: After Waller issued her order to leave Corto Maltese to its fate, Bloodsport turns his back to Starro that is wrecking the city and walks towards the camera. Just a moment before the cut, Margo Robbie is shrugging, a gesture that is supposed to happen in the next shot, and she in fact repeats it in the next shot a second later. (01:48:30)
Character mistake: David Dastmalchian is the Polka-Dot Man, hyphenated in the comics, and in the end credits of the movie. Then again, when Waller threatens to kill everyone off, the name of the character appears in print as Polka Dot Man, no hyphen. (01:49:40)
Other mistake: Despite being a deadly marksman (only a few minutes earlier in the movie he stopped a bullet directed at him shooting it off the air), Bloodsport snipes several times at the huge kaiju featuring a massive eye in the central part of its body, and never once hits it. (01:51:45)
Continuity mistake: When Polka-Dot Man shoots his projectiles at his giant mom, he's standing in the sun or in the shade depending on the camera angle. (01:52:45)
Answer: It's a combination of various reasons. Will Smith wasn't available to reprise his Deadshot role, so there was a shift in the story. King Shark was intended to be in the first film, but the CGI was too extensive, so they went with Killer Croc. In this film, they took the opportunity to bring in King Shark as the "monster" character. But, this film isn't really a sequel or reboot. Basically, this is a new storyline with new characters, and many of the previous characters are just not in the film, with no exposition on what happened to them, and they may not even be part of this film's "universe." The fact that some of the actors play the same character in both films only serves to muddle the concept of this film not really being a part of the previous film's continuity.
Bishop73