The sub commander indicates that they are responding to an SOS in the Atlantic, but when Steve Trevor informs Cyborg, he says the sub sank in the middle of the Pacific.
It had been stated that only the Atlantean Royal Family could wield the Trident, but the final scene showed an unnamed priest-like character coronating Arthur with it just before handing it back to him.
After Arthur is stabbed by the bar customer, the rip in his shirt is on the left side of his chest. In a later shot, it's more to the right.
At 45:48, as the League members are looking down towards Arthur and Atalanna, Superman's blue collar is skin-colored. Presumably, the colorist forgot about the New 52 design being used, and colored in the more classic look.
Screen titles identify the submarine as traversing the Marianas Trench, but Captain advises they are "investigating an SOS beacon in the middle of the Atlantic". The Mariana Trench is in the Pacific.
A drunk Arthur is talking to/fighting to protect and free a red lobster in a seafood shack. There is no instance where a live lobster will have a red shell. The red shell occurs only on contact with boiling water. Thus, either the lobster was dead and Arthur hallucinating, or the artists made an enormous colouring mistake.
Any of the JL without some measure of invulnerability should have been crushed while visiting Atlantis. There is no way that a simple breathing mask would have been anywhere near enough to protect Batman, Cyborg's human flesh, or The Flash from the pressure at that depth. In addition, Superman and Wonder Woman cannot breathe underwater. They should have been unable to speak, and forced to hold their breath during their sojourn under the sea.