When Felix and McElroy jump the Jaguar onto the garbage barge, you can clearly see that there is nobody there. Then, after the car comes to a stop and they get out, Popeye and his crew are just sitting there, a few feet away on the same garbage piles they crashed into.
SPOILER. Whilst Virgil Kane interrogates Leopold Durant, he tells Arthur to face front, pointing with his empty right hand, whilst holding his baton (which is inserted in Leopold Durant's left shoulder) in his left hand. When the scene immediately cuts to Arthur, Virgil Kane is pointing with the baton in his right hand.
When Dakota is driving to Vegas and talking to the Lizard on the phone, you can see the telephone poles passing by to her left. Then we see an aerial shot of her pulling over, and the telephone poles are on her right. When she turns around and the aerial shot pulls back, you can see the telephone poles are only on one side of the road, and would not have been visible to her left when she was driving the other way.
When Iky presents the weapons to Dakota in the hangar, a shadow is visible on the right-hand side of the bench on which the weapons are placed. As the camera moves backwards, so does the shadow, indicating it belongs to either team or equipment.
When they are in the box at Anfield (the Liverpool football club stadium) their box looks out across the centenary stand, suggesting that their box is in the main stand. However, there are no executive boxes in the main stand, the box would have to have been located in the centenary stand, making the view from their box impossible.
When Felix and McElroy go into the pub in Manchester, the sign outside says Manchester United vs Liverpool, suggesting that the game was being played at Manchester United's home, Old Trafford, whereas it's actually being played at Anfield, Liverpool's home stadium.
When Dakota and Felix are fooling around in the bath-tub, they throw their underpants onto the floor. Yet Felix still is wearing white underpants, visible for some seconds when he's turning around in the tub.
The goof item below may give away important plot points.
Incorrectly regarded as goofs
The chemical formula on the back of the postcard shows some of the hydrogen (H) atoms forming 2 bonds which hydrogen does not do. However, the chemical formula is a complete and total sham - a vital, integral plot point, so naturally it would have errors in it.