Welcome. We don't like touch-n-go deadlifts (for reasons explained in the book and probably around the forums). You need to put the bar back down and reset the back every time.
That said, looking at your first rep, when you set the back by lifting the chest, think of it as more of a steady "squeeze" into extension rather than "snapping" into extension. You're more likely to get all of the "slack" out the system. Also, keep the bar on your legs the whole time.
Five reps pulled from a dead stop each time.