Continuity mistake: After Batman shoots Reverse Flash through the head, Flash rushes over to Batman and catches him before he falls over from his wounds. As Flash is lying him down slowly, there is no blood on Batman's face. It then cuts to a close up as Batman reaches up to pull off his mask and there is suddenly blood on his lips and chin. (01:12:20)
Continuity mistake: After Aquaman finds Orm dead and sees the carnage of the battle, Wonder Woman comes up behind him and stabs his back with her sword. He falls to his knees and she walks around in front of him, and as she does you can see there is no blood on her sword. But then she holds the sword to his neck in a close up and suddenly the sword is covered in Aquaman's blood. (01:10:15)
Continuity mistake: After dodging a low attack, Wonder Woman jumps into the air and slashes down at Aquaman with her sword. Aquaman raises his trident and blocks the attack, but is only holding the trident with one hand. It cuts to a close up and instantly Aquaman is two handing the trident. (01:00:25)
Continuity mistake: After catching the rocket and saving Cyborg and Batman from it, Superman turns and drops the exploded rocket and begins lifting into the air. It cuts to a wide angle as Superman is hovering above the ground, and the rocket he just dropped is nowhere to be seen. (00:52:05)
Continuity mistake: When Barry is looking at the gun case in the Batcave, a cork board is visible in the background covered in raggedy playing cards. The one to the left of the center Joker card has blood on it, a lot of it around the bottom right corner of it. Later when Batman looks at the cards, the blood on that card is significantly less. There is also a card to the right of the Joker card that is torn with no blood on it. But in the close up when Batman is looking at it, that card now has a large blood spot in the center. The card symbols on the cards are also closer together, the cards above the Joker are significantly less damaged, and change from suit of hearts to a different suit. The entire board seems different. A few shots later, the cards above the Joker card are back to hearts again. (00:20:45 - 00:25:30)
Continuity mistake: When Wonder Woman is interrogating Steve Trevor, other Amazons are standing around her. Between shots when another Amazon appears, some of the Amazons' sword sheaths and other items on them change coloration. The one on the far right first has a gray sheath with a yellow tip, which then changes to solid yellow. Her collar also changes from yellow to black. And the one closest to Wonder Woman has a sheath that goes from a gray with yellow tip to a solid gray. The Amazon closest to the camera also has a quiver for her arrows. It changes from yellow to brown. And the one between the one with the yellow quiver and the one on the far right is wearing a white skirt with a black band around the waist. The band turns yellow. (00:22:40)
Continuity mistake: Wonder Woman tries to stab Captain Thunder with her dagger and just breaks it on his chest. She then has to drop the broken blade to catch his fist as he tries to punch her. She then uses both her hands to use her Lasso of Truth to make him say shazam and break his form. The lightning bolt hits her and she flies off him as he reverts back to 6 children. As she stands up, the broken dagger is suddenly in her hand again. (01:08:35)
Continuity mistake: Just after Wonder Woman and Aquaman argue a brief moment about her killing his wife, they continue their fight. Between the close up and the far shot, the rubble by the wall they are next to changes significantly in shape and amount. (01:00:20)
Continuity mistake: On Batman's plane, Flash walks up to Batman's seat, places his left arm on the top of it, stretches out his right arm to the side and says "Bruce's Batplane was a little more... stoic." It cuts to a close up of Batman and suddenly Flash's right arm is crossed with his left arm and his hand on his arm. It is still like that when it cuts away again. (00:55:50)
Continuity mistake: Batman and Cyborg have their backs to the tunnel they just came from and are shooting at the boats in front of them. Some soldiers come out of the tunnel behind them and fire a rocket in their direction. Superman suddenly jumps in and catches the rocket and it explodes. The blast knocks Batman over the rock he was hiding behind so he is on the boats' side of it, not the tunnel's side. But moments later when he is getting up and twp solders are rushing him, he is suddenly back on the side he came from, just before Superman vaporizes the soldiers with his heat vision. (00:52:10)
Continuity mistake: After rescuing Superman, Cyborg, Batman and Flash step out into the open and are quickly confronted by several heavily armed boats full of government people. There are boats in front of the four of them and none to the side. But when Cyborg steps forward saying he can resolve this peacefully, two boats suddenly appears to their left slightly behind them. Then when the shooting starts, those two boats vanish. (00:51:10)
Continuity mistake: When Flash, Batman, and Cyborg walk into the cell that is holding Superman, a shot of just Superman's legs show that they are down with his knees on the floor. It then cuts to an angle from the trio and suddenly his legs are bent up and his knees in the air. (00:49:35)
Continuity mistake: Wonder Woman stands on top of Captain Thunder and uses her Lasso of Truth to force him to say Shazam, breaking his transformation and turning him back into the 6 kids. This causes lighting to come down and strikes Wonder Woman, sending her flying and sliding across the ground. When she comes to a stop, her hair is draped over her head. The next shot, she begins lifting her head and her hair is suddenly behind her head down her back again. (01:08:55)
Continuity mistake: While walking through the sewers, Flash is holding up Superman and beside Cyborg. Cyborg tells Superman that there are heroes, and Superman looks up at him asking "Heroes?" The next shot is from a different angle, and Superman is suddenly looking down again. (00:50:35)
Continuity mistake: As Batman makes his entrance into the Flash museum, he does so by busting through a skylight window. As it breaks and he somersaults down, you can see a load of large chunks of glass and metal framing falling all around Batman. But moments later when he lands, only a few small shards hit the ground around him. (00:06:50)
Continuity mistake: As Cyborg is opening the door to Superman's cell, several layers of blast doors open one at a time. The last one to open you see for a moment as it begins to slide, you can see the room beyond through it in red. It then cuts to the other side and suddenly there is yet another layer of door that is opening by just sliding to the right, preventing any possibility of a view seen less than a second before. (00:49:30)
Continuity mistake: When Reverse Flash stabs Flash in the leg with a piece of rebar, Flash is on a small pile of rubble. He takes the bar out and drops it on the rubble. But then it cuts to a different angle as Reverse Flash continues to assault Flash, and suddenly Flash is in a different location, with no piles of rubble in his immediate area. (01:04:50)
Continuity mistake: In the beginning of the film when young Barry's mom is telling him about grandma's prayer, the shot of the side shows Barry's mouth is closed. But when it cuts to his face close up looking confused, his lips are parted and his teeth are showing. (00:00:35)
Continuity mistake: During their fight, Aquaman gets off a good kick on Wonder Woman and sends her flying backwards. She hits the ground and starts sliding. She goes between two other Amazons before stopping. It cuts to a close up and suddenly the Amazon on her right that she slid past is suddenly where she has not slid past her yet. (00:59:45)
Continuity mistake: When Flash takes off running in the desert trying to test if he can break the sound barrier, the lightning bolt on his chest is much wider than seen just a couple of shots later. (00:42:55)
Answer: Flash couldn't travel through time later in the movie not because Zoom was alive but because Zoom was also tapping into the Speed Force, preventing Flash from gathering enough of the Speed Force to break the Time Barrier. When Flash originally went back in time it's likely because Zoom was in custody, therefore not tapping into the Speed Force at that time.