Logan Lucky (2017)

Clyde Logan: Did you say Cauliflower to me?

Question: When the prosthetic arm of Clyde was sucked into the hose, Jimmy told him he would go back and get it from the vault, which he didn't. So the whole movie I was thinking: why did the FBI agent fail to find the fake arm? But in the end it is shown the attachment was in the machine all along. How did it get there? The hose was firmly embedded in the tube and was sucking all the money out of the vault. The prosthetic limb should be lying in the vault somewhere, but inexplicably it was not?