At 1:54:0 Batman is holding the top of the ID card but in the close-up he's holding the bottom edge.
Just before the Mother Box explodes, Cyborg is drenched in sweat. When Cyborg is coming back together just before Flash touches him, his skin is completely dry.
When Barry Allen goes undercover as an Air Force member the ID card terminal identifies him as a member of the "Military Police." This term has not been used by the Air Force since 1947. It should actually say "Security Forces." Also, it identifies him as an E7 (Master Sergeant), Barry is a little young for such a senior NCO rank.
A powerful bomb that is about to destroy four "city blocks" from inside a bank, does not explode harmlessly just above the roof of that bank.
In the climax of the movie when Steppenwolf is being pulled down by Wonder Woman and Aquaman. When he falls he lets go and loses his ax/weapon yet when lands he used it to stop himself from sliding.
The children scream in horror when Black Clad Alpha opens the suitcase. But from where they are standing, there is no reason that they should instantly recognise it as a bomb, it would just look like he opened a suitcase with some metal things inside. They would not be able to see the explosive and probably wouldn't recognise it anyway.
In the epilogue, Lex Luthor offers Deathstroke "a glass of Goût de Diamants" champagne. However, the glasses contain only the tiniest sip of wine.
At 2:26:49 during a security checkpoint as Barry drives a truck sneaking the other Justice League members into the STAR Labs facility, a guard brings up Barry's personnel file, which includes the misspelling "GOVERNMENT DIVSION".
The movie doesn't explain why, when visiting Lois Lane, Martian Manhunter disguised himself as Martha Kent (Superman/Clark Kent's mom).
When the Flash runs in circle to "charge", he tripped (3:23:51) by the resulting blast from an energy weapon. However, with his speed, the blast would be just another obstacle he should have been able to avoid while running.
1:39:49 When Dr. Silas Stone sees the metal sample from the alien spaceship being super heated, bombarded with x-rays from the electron-laser, making it the hottest thing on earth, he exclaims: "3.5 million kelvin!" (K) but on the screen he is pointing at the temperature is given in Celcius (C°).
The Black Clad member says that the bomb will destroy "four city blocks". London is not laid out in blocks like an American city, instead, the streets are in random patterns that are centuries old.
When Clark and Bruce are at the Kent farm, having bought it back from the bank, Clark is not wearing his trademark glasses. Without his glasses, he should have been recognized as Superman.