Visible crew/equipment: When Owen runs towards the raptor gate, a moving boom mic shadow is visible on the gate. (00:23:30)
Visible crew/equipment: When Masrani puts his sunglasses on you can make out a camera reflection in the glass. (00:15:10)
Visible crew/equipment: When Claire and the soldiers are running to shoot the birds, a camera shadow can be seen on her briefly. (01:22:00)
Visible crew/equipment: When Lowery says "that first park was legit" two light screens are reflected in his glasses. (00:11:30)
Answer: Chances are either the gates were left open after the Pterosaur attack to allow visitors to escape quickly, or Hoskins had left them open earlier and forgot to close them to try and justify using the raptors as weapons.