Continuity mistake: After Barry wakes up in bandages with third degree burns all over him, there is a spot of blood on his chest below his left shoulder. A good amount of the blood stain overlaps a line dividing two strands of the bandage. Moments later when he sits up, the blood is barely above that line at all. Later when Barry is sitting in the chair again, that same stain has completely changed shape. Other patches of blood on him also change. (00:36:20 - 00:38:00)
Continuity mistake: Lois hides under a purple car. It becomes red after a beast walks over the bridge. (00:39:15 - 00:39:45)
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: 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)
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: The Flash trips in a field with loads of cacti. One of them changes in appearance between shots. There is also a two foot tall cactus with no branches next to it that disappears. (00:43:10)
Continuity mistake: The Flash is back at Wayne Manor with Batman, after regaining his powers. In the wide shot of the Manor's interior, the windows are about 5 feet in height. The next shot shows the windows now only about two and a half feet in height. (00:45:05)
Continuity mistake: When The Flash is on Batman's computer, the number of windows cracked/smashed changes between shots. (00:45:10)
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: At the meteor crater in Metropolis, Flash and Batman are standing very close to the edge of the roof of a building. A few shots later, they are about twice as far from the edge. And then there is suddenly enough room for Cyborg to land between them and the edge, and Flash be able to take a few steps forward towards Cyborg. (00:46:15)
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 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: 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: 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: 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: 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: 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: 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: After Wonder Woman smashes Aquaman through a wall into a building, he elbow drops onto her and then smashes her face into the floor, leaving a hole. The it cuts to a wide angle and he picks her up to throw her. The hole left behind from her face is now gone. (00:59:55)
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.