Continuity mistake: Flash uses a speed boost of energy in his arm to fling the gray adhesive substance at Reverse Flash, slamming him into a glass display case and trapping him to it. The glass of the case breaks and cracks and the cracks around Reverse Flash's head are quite large. But after Batman makes his entrance and grabs Citizen Cold, that shot shows the cracks a lot smaller and shorter. They are back the way they were in following shots. (00:06:55)
Factual error: When the rest of the Justice League arrive at the Flash Museum, Captain Atom vaporizes a section of the wall to allow him and some others to enter. The hole shows 3 layers to the wall, the inner wall, the outer wall, and a middle apparently metal center section. There are several circle like spots around the hole in the center part of the wall. They are all perfectly round, despite being in any given direction around the circumference of the opening. This is wrong. The circles would be caused by structural bars inserted in the layer, and they would all have been either vertical or horizontal, and thus the circles would not be circles all the way around, but changing to elongated and shorter depending on where they were on the opening. Yet all are perfectly round. This would mean that the all the bars were in all different directions and converging in the center of where Atom just happened to make the hole, which would never be the case. (00:07:05)
Character mistake: One of the top most taboo things for a super hero to do is reveal any aspect of another hero's identity to someone, especially a villain. But when Flash is trapped by the gray adhesive and the other Justice League members are about to take the villains away to disarm the bombs, Flash tells Green Lantern "Hal, go", calling Green Lantern by his first name right in front of Mirror Master. (00:08:05)
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: As Superman is escorting Reverse Flash out of the museum and down the stairs, Reverse Flash is in front of Superman, but adjacently to his right. The shot cuts to over Flash and Batman's view as Superman and Reverse Flash stop walking, and now Reverse Flash is almost totally in front of Superman. (00:11:10)
Revealing mistake: After the museum battle, Barry wakes up at his work and looks at the computer screen at an article reading WORLD FACES ARMAGEDDON. Look closely at the blocks of text under it. It is the same lines of text repeated over and over again. (00:12:10)
Continuity mistake: After the guy wakes Barry up and hands him some coffee, he says he doesn't mean to interrupt Barry's beauty sleep, and Lord knows he needs it. In the middle of this sentence, Barry is holding the cup close to his face, but stops short of taking a drink and looks up at the guy who handed it to him. It then cuts to a close up and suddenly Barry has the cup to his mouth taking a drink. (00:12:20)
Revealing mistake: Barry is handed a file at his work. He starts reading it but the paper is totally blank. (00:12:35)
Other mistake: The television news report about the battle between Captain Boomerang and Citizen Cold has a message scrolling across the bottom. The problem is that the words are moving from left to right, which forces the viewer to read the message backwards. (00:12:40)
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: 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)
Revealing mistake: In Flashpoint Batman's first scene, he is shown fighting Yo-Yo. At one point during the fight she wraps a rope around his neck and tries to strangle him. At the end of the fight, he takes the rope off his neck. The rope goes through his neck when he does this. (00:16:20)
Continuity mistake: When Batman is interrogating Yo-Yo, he begins cracking her visor. The cracks disappear when Cyborg catches her. (00:16:45)
Other mistake: Cyborg confronts Batman about throwing Yo-Yo off the roof and then turns on a hologram projector in his arm to show other super heroes. There is a beam emitted from his arm generating the holographic images. We then see him turn the beam off, yet the holograms remain and they have a conversation with them. (00:17:55)
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: 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: Barry breaks into Wayne Manor. He moves the grandfather clock and goes down the stairs to the Batcave. There is a bottle on the stairs. He is about 5 steps away from the bottle in the first shot, but only 1 step away from the bottle in the next shot. (00:20:30)
Continuity mistake: Barry is looking at a picture of the Wayne family before Batman punches him away. Barry is knocked to the left towards a bed. The photo was positioned so it was facing to the right. A few shots later when Batman is holding Barry by his collar, the angle shows them by the bed and the camera is behind the table the photo was on. But the photo is facing the camera. At this position of the camera and photo compared to previously when Batman punched Barry, the photo should have been facing away from the camera. (00:20:40 - 00:21:20)
Continuity mistake: As Barry is in the Batcave, he looks at a gun in a case and says "What happened to you, Bruce? You were the James Bond of superheroes." The camera pans over to a picture frame and you can see behind it there is a beer bottle. But a couple shots later from a different angle, the beer bottle suddenly changes positions behind the photo. (00:20:40)
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)
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.