Other mistake: The janitor, Howard, stops Dr. Stone to talk to him about the loss of his son. Look at his badge; the person on it sports a beard and sideburns and a hat, and it's "Jensen" plus initial. Later on the same janitor hears a noise inside the lab and you can see the badge picture is different and it lists the full first and last name. The first scene was a Whedon reshoot, so probably after weeks they didn't have the original prop and made another one. (00:18:55 - 00:21:15)
Continuity mistake: Flash is running to power up Superman's ship. In the wide aerial shot when he dives towards the pool (after he went past Cyborg and Aquaman with their backs turned to him) notice Diana with hair in front of both shoulders. A close-up with her and Arthur follows and her left shoulder is clear of hair. (01:12:10)
Character mistake: When the military security checks Flash's phony badge, his false name "Rowe, Wesley" replaces the name of one of the names in the list to the right, one "Choi, Wesley." The problem with this is that the last names this way are not in alphabetical order anymore, so Cyborg made in fact a rather poor fake, especially for such a supposedly super-powerful being who hacked the Bat-cave computer on the fly, on top of a much larger mistake with the date of birth listed as 11/06/10, and the movie is set in 2017. (01:09:30)
Continuity mistake: After the underground battle with Steppenwolf when they are finally joined by Aquaman, Wonder Woman sums up the situation with "All he needs now is the Lost Box of Men." Batman replies "If he doesn't already have it" in another shot, where Diana's hair is missing in front of her shoulder. (01:01:15)
Continuity mistake: Clark is thanking Bruce for the house. They both look in the distance at Lois and Martha; there are a couple guys fetching boxes near the carpenter, on both sides of the workbench, but they are nowhere to be seen in the new closer angle. (01:45:55)
Other mistake: The security guard alerts Batman about Barry Allen's arrival pushing a button on his phone. The date on the phone says it's Friday 20th Jan, which is coherent with the year (2017) this version of the movie is set in, but too early for the K-pop "As if it's your last" music video playing in Flash's lair (it was a summer release). (00:16:50)
Continuity mistake: When Dr. Silas Stone is speaking with Victor, he is wearing a completely different set of clothes from what he was wearing at the lab in the scene just prior. It is implied that the scene happened immediately when coming home from the lab.