Continuity mistake: There is a large Flash symbol on the wall where Flash is trapped. The distance between this symbol and the ceiling changes a few times in the scene. It also changes position in relation to the display case Reverse Flash is trapped against several times in the scene. (00:04:25)
Continuity mistake: There are some large cracks on the wall left from when Captain Boomerang pinned Flash to the wall for a moment. When the gray adhesive traps Flash against the same wall again, the bottom most crack is to the right of his head. Then when Flash begins vibrating his arm to throw the adhesive and the bomb at Reverse Flash, the crack is suddenly on his left side. It switches back and forth during the scene. (00:05:00 - 00:06:25)
Continuity mistake: After freeing himself from the wall where he was pinned with boomerangs, Flash takes off as Captain Boomerang and Captain Cold continue to attack him. Cold shoots ice on at him that gets on the wall. A few moments later when Flash hits that wall again after his foot is frozen, the ice that Cold put on the wall moments before has vanished. (00:04:30)
Continuity mistake: At his mother's grave after his wife tells him he was just a boy, Barry Allen raises his right hand and says he might have been able to stop it. There is no ring on his hand at that point. Then when he takes off running after his device alerts him to a break in at the Flash Museum, there is suddenly his ring on his right middle finger, out of which he pulls his costume. (00:02:40)
Continuity mistake: After opening the door at his mom's house, young Barry is shown in a close up of his face. A white fence is seen behind him with red bushes all around the front of it. Moments later when the camera is pulling back in a different shot to show his mother's corpse, the same fence is visible, but now with no bushes in front of it. (00:01:25)
Revealing mistake: When young Barry walks into his house and discovers his mother's murder site, he drops a book on the floor and a birthday card falls out. The book opens when it hits the ground and is towards the middle of the book, yet the pages are completely blank. (00:01:35)
Continuity mistake: After he gets his powers back, Flash takes off to try and time jump with speed. He fails and trips, sliding to a grinding stop out in the open desert. The shot from the side of him on the ground shows him lying on rolling "sand waves" and looks rather smooth with no vegetation around him except some cacti in the distance. The shot then cuts to an over head view as he sits up and starts to weep in desperation. Suddenly the rolling sand is now a dried cracked dirt and there are bushes and more cacti around him. (00:43:10)
Continuity mistake: After Reverse Flash stabs Flash in the leg with a rebar, and Flash retaliates by smashing a rock in Reverse Flash's face, watch Flash's hand. There is a rip in his costume on his right hand over his index finger knuckle when it cuts to a close up of him reaching for the rebar. But the previous shot shows no rip on his hand. (01:04:45)
Continuity mistake: Overlooking the crater left behind by Superman's ship in Metropolis, Flash and Batman are standing on the roof of a building with concrete tiles. The tiles change in size a few times during this scene, most notably bigger when Cyborg looks up at a satellite. (00:46:10)
Continuity mistake: When Barry lays flowers at his mother's grave, the base of her tombstone changes style between the close up and when he stands up and runs to his wife. (01:15:25)
Continuity mistake: While fighting Black Manta, Batman stands next to an orange car as he blasts away with his pistols. Between shots, the front seats of this car change from separate seats to a bench seat. (01:01:45)
Continuity mistake: When Flash goes around the decapitated statue of himself in the Flash museum, he stops and you can see a glass door behind him that is broken. The bottom-most part of the break is not to the bottom of the door frame, but a few inches to half a foot away. It then cuts to a view of his feet, and you see the same door behind him. Now the bottom part of the break in the glass is now right at the bottom of the door frame. (00:03:25)
Continuity mistake: Reverse Flash smacks Flash over to the edge of a building. The building is heavily damaged from the war and crumbling. The edge is broken off and jagged, but averages out to a straight line. A few moments later, when Reverse Flash puts his foot on Flash, the broken edge of the building has become much more jagged and uneven. (01:05:40)
Continuity mistake: After Reverse Flash stabs Flash in the leg with the broken rebar, Flash picks up a rock and slams Reverse Flash in the face with it. In the wide shot of this, the rebar is a solid gray bar. It then cuts to a closer shot as Flash grabs it, and suddenly there are screw like lines swirling around it. (01:04:45)
Continuity mistake: Reverse Flash stabs Flash in the leg with a broken rebar. In the side shot, Flash throws his head back. It cuts to a close up of Flash, and he throws his head back again and screams. It cuts several times between a close up and a side shot at this point. In the side shots, Flash has his lips open, but gritting his teeth hard. In the close ups, Flash's mouth is wide open. (01:04:40)
Continuity mistake: As Superman is escorting Reverse Flash down the steps of the museum, you can see the top part of Reverse Flash's red lighting symbol over lying the black circle and extending up into the yellow of his suit a few inches. It then cuts to a different angle and the tip of it is barely a few millimeters above the black circle. Also between shots, the bottom yellow triangle part below the S on Superman's chest suddenly gets much larger. (00:11:10)
Continuity mistake: Just before Aquaman can stab Cyborg's heart, Superman cuts off his arm with laser vision and it falls to the ground beside him with the trident. A little later when Cyborg dies and Superman is kneeling beside him, it cuts to a wide angle. Aquaman's arm and trident are nowhere to be seen. It was not blown away by Superman's breath either. (01:09:50)
Continuity mistake: Reverse Flash knocks Flash back and he is next to the edge of a building, his arm hanging over the side. Flash sees Grifter get killed and tries to get up, but Reverse Flash presses him back down with his foot. Flash is still right next to the edge of the destroyed building. The Reverse Flash zooms around behind Flash, and suddenly there is at least a good 2 feet between Flash and the edge. Moments later, Reverse Flash kicks Flash and he goes over to the edge again. (01:05:40)
Continuity mistake: After the car falls on Batman, Grifter begins shooting at Black Manta. He is standing on top of a yellow car. When Black Manta begins shooting heat vision at him, the car turns green. (01:02:05)
Continuity mistake: While Batman is fighting Black Manta, he dives over as the bad guy blows a car into the air. The car is a light blue color and falls over on Batman. The next shot as Black Manta is walking towards it, the car has turned to a light orange color. Moments later when Batman crawls out of that car, it is back to being light blue. The car it lies on also changes from purple to orange. (01:02:00)
Chosen answer: Despite the ending in Flashpoint to indicate a Darkseid invasion, War is not a sequel. It's a reboot. While both films were part of the DC Universe Animated Original Movies series, War is the first movie of the series that is now part of the DC Animated Movie Universe. This is also why the voice actors are different.
Bishop73