In the scene after the mutants escape and one is seen jumping from a high platform Jason is seen holding a M4A1 rifle. The next scene he is shooting the mutant but is now holding a G36k
While mercenaries chase down Valerie and Jack with boats, Parker's pistol is shown to be empty in close shot (slide is locked to back-position). In the next cut the weapon is reloaded again (slide is where it is supposed to), but in the next shot immediately after it the gun is empty again.
In the end scene when Jack Carver is walking away from the couple the sound guy and his microphone are visible on the boat.