Deliberate mistake: Spoilers! When Black Manta is defeated, he is knocked unconscious and tumbles down a rock face after his helmet explodes on his face into the waters by the shores of Sicily. These currents and waves at best would have carried him to the rocks or the beach, leaving him on land or near it. However in the after credit scene he's somehow found out in the middle of the ocean on a broken drift wood. He would not have been carried back out to sea like that.
Suggested correction: The water is tidal. If the tide was going out, the current would take him out to sea.
There are hardly any tides in the Mediterranean Sea http://scienceline.ucsb.edu/getkey.php?key=995.
Deliberate mistake: When Nico finds Hilda's body at the start of the movie, her left arm is shown next to her body, and her right arm is outstretched. When her death is shown later in the movie, both arms are outstretched when she lands on the floor. (00:05:50 - 01:30:55)
Deliberate mistake: Luke had a box of T-shirts he designed and Faith reached into the box and removed the top T-shirt. Without looking at the size or even holding it up to her body to see if the T - shirt would fit, Faith asked, "How much?" Luke replied, "Ten" [dollars]. Faith reached into her pocket, pulled out a wad of bills and handed it to Luke without counting the money. Faith put the T-shirt on over her top and it was a "perfect fit." (00:03:55 - 00:04:37)