Continuity mistake: The bridge Lois hides under has several impact holes on the side of it from the war. These holes change in number and position in different shots of the bridge. (00:39:35)
Continuity mistake: While hiding from the Amazons under the bridge, Lois Lane hides by a purple car. There is an upturned blue car on the opposite side of the bridge there as well. This car disappears when the Amazons jump down to her and reappears again in the scene, also changing position a few times. (00:39:40)
Continuity mistake: After fighting for a brief few seconds, Black Manta kills Deathstroke by burning a hole through his chest with his heat vision. Deathstroke falls right next to Lex Luthor as his chest sizzles and his swords fall around him to. A couple shots later as Black Manta is picking Lex up, Deathstroke's body and swords have vanished. (00:29:35)
Continuity mistake: On the deck of the Ravager, there is a large flak cannon that one of Deathstroke's men turns on Aquaman's forces. One of Aquaman's men destroys this flak cannon into a large ball of fire. Then a guy stands back up and turns into Clayface and begins absorbing some of the enemies. Orm uses his staff to obliterate this guy and behind him is shown where the cannon was. There is no fire, debris, or any sign of the destroyed flak cannon. (00:28:35)
Continuity mistake: Once Aquaman's forces begin attacking the Ravager, people begin dying left and right from both sides all over the ship. These bodies keep disappearing as the fight goes on. (00:27:30)
Continuity mistake: As Lex Luthor is discussing the shockwave epicenter with Deathstroke, he places his finger on the computer screen about an inch away from the Epicenter blip down to the left just as the orange moving blip begins going across the screen again. The orange blip makes it almost to his finger before it cuts to a close up of the screen. Now suddenly Lex's finger is much further away from the epicenter blip and sliding to the right, with the orange blip in front of his finger. (00:26:40)
Continuity mistake: After Wonder Woman snares Steve Trevor with the lasso and begins interrogating him, the other Amazons that were chasing him walk up in front of Wonder Woman. There are 5 Amazons there, including Wonder Woman. A few shots later when she's holding Steve up, a 6th Amazon girl suddenly appears with the other 4 that were in front of Wonder Woman, standing almost behind Wonder Woman but to the side. (00:22:40)
Continuity mistake: When Steve Trevor is running from the Amazons in the destroyed Big Ben, he leaps from a ledge and crashes through several boards on the way down as he shoots back up at the Amazons. When he hits, he rolls to his feet with broken boards all around him and several arrows hit the ground that the Amazons fired. When he takes off running and shoots back at them again, you can see the Amazons jump down to that very same spot before Wonder Woman's lasso catches Steve. The broken boards and the arrows have vanished. (00:21:55)
Continuity mistake: As Barry slides the grandfather clock to the side to get to the Batcave, a large plume of dust boils up around the top. It cuts to a view of this from the other side in the Batcave and there is no dust in the air at all. (00:20:30)
Continuity mistake: When Barry enters the Wayne mansion, he goes to a large grandfather clock to move it out of the way, gaining access to the Batcave. As he walks up on the clock, the glass on it has no visible imperfections except being covered in dust. It cuts to a close up of the clock as Barry begins pushing it aside and suddenly there are scratches and smudges all over the glass. (00:20:25)
Continuity mistake: Finally defeating her, Batman throws Yo-Yo down on the ground and she is on her side. One of her pigtails is draped over her head towards the back of her head. The shot cuts to Batman walking up to her and suddenly the pigtail is in front of her face. (00:16:20)
Continuity mistake: After falling down the stairs and seeing his mom alive, Barry stands up and turns completely towards his mother. The shot cuts to a different angle at close up, and he has to turn his torso towards her now. (00:13:25)
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)
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)
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.