Given the density and other characteristics, gold is a poor choice for barbell material and would dent easily. This happened when the barbell fell out of the the truck in the chase scene but should have been more extensive and visible than just a bent bar and loss of some paint.
When the bad guys take the bait to come steal the 300-lb barbell, after they smash the glass they lift the wooden frame, and one side of the frame easily lifts the barbell as they move it.
The Harts set up an opportunity for the thieves to break into their house and steal the barbell, knowing that there will be broken glass all over their upholstered furniture and Persian rug.
Jennifer said that she's going to finish exercising and shower, and get to LAX in 40 minutes. That's impossible.
Max had gone to the gym to take a sauna, but Jennifer opens the door to go in, even though Max might have been partially or fully undressed.