(at around 16 mins) When Elektra is in a bikini after swimming, her wound can be seen on the top of her stomach. However in the previous scene, when she is underwater, there is no wound.
(at around 57 mins) In one scene, Stone throws his wooden club to Elektra. In the next shot, he attacks Abby with his club which he didn't get it back.
At around 56 minutes, Elektra breaks the main blade of one of her three-pronged sai swords on the back of the Stone character, but shortly thereafter, when Abby tries to steal Elektra's sai, both are in perfect shape. Elektra is never seen replacing or repairing the broken sai.
(at around 40 mins) Stick takes his shot while playing billiards and the cue ball stops near the eight ball. Before Stick takes his next shot, white ball is far away from eight ball.
(at around 12 mins) During one flashback, Elektra goes back to her ride in the ambulance when she dies. The paramedics use a defibrillator on her. A defibrillator is only supposed to be used on bare skin but they have it being used over a leather vest. (This was most likely done to help connect the flashback to her final scene in Daredevil by showing the costume she wore that night.)
The fact that almost every movie depicting a character associated with Greece is misusing the greek alphabet for example (capital sigma instead of E). Another example is Elektra's necklace that instead of H capital lamda EKTPA writes E capital lamda EXTPA. Movies are not meant to be shown only in countries that ignore the greek alphabet and it is rather offensive for the greek viewers.
(at around 34 mins) When Elektra is talking to Mark after she finds out he and his daughter are not who they say they are, she says, "Who are you? Don't lie to me." When she says "Don't lie to me," her lips are not moving.
(at around 46 mins) When Elektra, Mark Miller and Abby arrive at McCabes ranch house and go inside, McCabe is standing there, looking at the hawk on the fencepost; you can see quite blatantly the anklets around the hawks legs and rope connected to the holding the hawk in place.