Parzival doesn't count to 3 before throwing the Holy Hand Grenade.
People would not be oriented the same inside the Oasis as they are in the real world. This problem was evident throughout the movie, and at its worst, was during the final battle on planet doom. Even if you could argue that the 6-ers were to start out in some sort of strict formation in the war-room as well as in the Oasis(unlikely), the further the battle rages, the more shuffled they would be with 6-er avatars 'zeroing-out', others filling any available spot in the war-room, and making the MechaGodzilla shaped red mark in the war-room impossible, and the cataclyst zeroing-out the whole war-room in a wave pattern the grand-finale of this specific blunder.
After Sorrento unleashes the cataclyst in the Oasis and goes back to the real world, he kneels in pain from the haptic suit's crotch panel, then he gets up and tears the panel off. As he walks through the door, the crotch panel is back in place, and it appears as if he is reaching for it again.
1) During the 2029 scene of Halliday and Morrow, the type, orientation and cleanliness of the bottles and plates on the tables around them change a few times during their conversation. 2) Later, in the scene where Halliday and Morrow are talking about the date with Kira, the scene is paused while Curator, Art3mis and then Parzival step away for a side discussion. When Parzival pulls Art3mis away from Curator to talk some more, Halliday and Morrow are missing from the room and the table has changed orientation, but when Parzival starts to step back towards the scene, it is back to the same state as when it was shown paused.
When Aunt Alice gives Wade the ultimatum that if he took her equipment again she would kick him out, she is kneeling next to his feet, even with the counter. When the scene cuts to behind her and she gets up, she is about five feet further away from him, past the counter.
During Sho's first speaking part in the 'Shining' challenge, the tassels on the handles of his swords are frozen in a downward position, but every other time it shows them, they swing as if with real-word physics.
While researching Karen Underwood Morrow's death, Wade views two different newspaper obituary clippings side-by-side. Much of the text in both is identical, but the left one says, "Mrs. Underwood was Fifty Six years old at the time of her death," while the right one states, "Mrs. Underwood was Fifty Nine years old" in the same sentence. (59 is probably the intended age, as the right-hand article also shows "1975 - 2034" in the headline.)
When Wade receives the message in his van from Nolan Sorrento he has the gloves from the X-1 Boot Suit. After his conversation with Nolan Sorrento as he is running back and calling his Aunt to warn her Rick answers the phone. It is shown that he is wearing Wade's X-1 including the gloves that Wade previously had in his possession.
On the scene set in the town against brick buildings, there is a banner for a car park with a United Kingdom 0121 telephone number on it. The film was shot in Birmingham (UK), but they did not digitally remove the telephone number.
In a chase scene about 1 hour and 29 minutes through, you can see a Nationwide Building Society branch in the background. As Nationwide Building Society is a mutual organisation based in the UK it would not exist in Columbus Ohio in 2045, and even if it did the branding would have changed by then.
When Perzival is playing Adventure he obtains the invisible dot without using the magic bridge.
When Halliday shows his younger self playing video games on a ColecoVision, there are only Atari 2600 cartridges spread out on the floor. However there are no ColecoVision cartridges lying around, nor does young Halliday have the "ColecoVision Expansion Module #1" necessary to play the prior-generation Atari games on the newer-generation Coleco console.
At the beginning of the movie, when you see the scene where James Halliday announce the Easter egg as Anorak the All-knowing, he says "Reveilling 3 hidden keys to 3 magic gates", but in fact, there is only 2 gate at the end.
When the Cataclyst goes off, everyone dies and then we see a glimpse of the big scoreboard being updated. Number 3 on the scoreboard is SORRENTO with two keys and 124,000 points, even though he should have been zeroed-out when Art3mis blew him up along with Mecha-Godzilla. However, the explanation is clearly implied, since we know that Sorrento never actually won any key - he had a bunch of his Sixers do the work and then took the keys and points from them, either by ordering or killing them. He must have done it again after being zeroed-out, so he would be the one to open the final door and get the egg the moment another Sixer got the third key. This explanation is further evidenced by the fact that numbers 4 and 5 on the board are Sixers and they have exactly the same score as Sorrento, implying that they are simply copying each other.
The junk pile of crushed cars seen at the beginning doesn't seem to have acquired a single model of car newer than about 2010, despite the whole pile sitting there up until 2045.
Correction - Its not actually mentioned in the movie but the cars seen are abandoned cars that the occupants of "The Stacks" arrived in (they ran out of fuel so were basically useless) and were then pilled up by the cranes used to make the stacks of mobile homes. It could be that the ones we see are simply from the first arrivals or that older cars were more affordable.
When Samantha is in Sorrentos rig, she finds a receipt for the orb of Osuvox with the instructions. Sorrento didn't buy the orb of Osuvox, Irok got it from the steampunk pirate therefore there wouldn't have been a receipt or any instructions.
The Sixers are likened to drones, no names, no identity, to the point that when they zero out, they can jump to another rig and carry on as if nothing happened. However, when Samantha/Art3mis uses the rigs (and the loyalty pod), her usual Avatar appears in the oasis, although no obvious facial scanning takes place. Furthermore, she's also able to access her personal inventory (And change her appearance) even though she's on the IOI Sixer account.
When Samantha is captured, she's informed that all of her outstanding debts have been consolidated and she's to be moved to a loyalty centre. However, IOI didn't think to requisition her Oasis possessions as she's able to access her personal inventory to use her drone orb to talk to the Orb of Osuvux.
Near the end of the movie, a policeman gets back into the left hand drive Columbus Ohio police vehicle on the right hand passenger side, incorrectly its black steering wheel is seen, indicating that the police vehicle is not left hand drive.
In one of the early scenes, during the reveal of the interior of Wade's secret van hidden under a bunch of crushed cars, he hooks up the battery while narrating about living with his aunt Alice and you can see a shadow cut across the light beam hitting his leg. The shadow doesn't completely clear the beam of light before it comes to a stop, still leaving shadow. In addition, a fully obscured van wouldn't have that much light coming in through the windows.
During the final chase scene, the vehicles involved can be seen driving up and down the same street several times, evidenced by the dark bricked structure along on side of the road in shots supposedly several miles apart.
When Wade is looking at the newspaper clippings that adorn the walls of his secret hideaway, the camera zooms in on a clipping about the death of Kira. The clipping directly to the left is made up of virtually the same text of the article, repeated over and over.
When Parzival first contacts Aech in the Oasis, the computer locates him on Planet Doom in Sector 12, but the on-screen graphic places Planet Doom in Sector 04. Additionally, at the end of the film, the High Five discuss that IOI solved the third riddle and located the fortress on Planet Doom in Sector 14 (number ultimate  divided by the number magic ).
When the High-5 exit the back of the van to a cheering crowd, it's snowing quite heavily. It's still snowing during the tracking drop shot to Sorrento being put into the back of the police car. However, in the very next show where Wade is talking to Og, the snow has abruptly stopped and doesn't happen again. As the scene was shot during winter at Leavesden Studios, it's very likely the snow was real, and therefore impossible to schedule.
During the Gold Ballroom scene, Art3mis (Olivia Cooke) asks the woman Kira (Perdita Weeks) to dance, and instinctively stands with her arms moved into the correct position to ballroom dance with a male partner. This is completely in line with her character, because she is in fact a woman, and the situation is very confusing in terms of gender. Indeed, her facial expression shows confusion, further indicating that this mistake is deliberate.
After Sorrento has been outed as the one who ordered the assault on The Stacks he casually walks in to stop Parzival from obtaining the Easter egg. He is quickly surrounded by the residents of The Stacks but pulls out a gun and everyone backs off. Despite being significantly outnumbered he keeps the gun pointed up and no one in the crowd tries to stop him. This is actually a very natural behavior. Yes, Sorrento has no chance against the crowd, but he will probably kill the first couple of people who rush forward and no one wants to be among these first ones, so no one moves. However the way Sorrento is holding the gun though with his finger on the trigger the many people he walks past could've easily grabbed his arm since he wasn't able to see from behind himself.
When Parzival begins the stage 1 race for the second time, he reverses dramatically and drops to the secret underground track. As he's getting his bearings and looking around in wonder, he steers right (in reverse) while still looking everywhere except the very narrow track he's driving on. If that's the first time he's driven on that road, he wouldn't know which direction to steer in, especially in a DeLorean with a flux capacitor blocking the rear window.