1. If pressure is applied to the lens barrel while the lens is mounted to the camera (pressure can be applied even while attaching the lens cap while carrying the camera with the lens attached in a bag), the autofocusing function of the lens may stop working.
When I tried to update the lens firmware with my 5D Mark III, the lens firmware update actually failed and froze at 31%, thereby locking up the entire camera. I had to actually pull the batteries out of the camera to shut off the camera. I checked on the Canon Forums and the lens firmware process is flaky and will result in a ‘bricked’ lens (shows up as firmware 0.0.0 and does not function).
But do not panic if this happens to you. Simply unmount the lens from the camera. Turn on the camera and delete your registered batteries. Turn off the camera, remount the lens, and turn the camera back on. Repeat the lens firmware update process and it will work and finish to completion.