Hard to say what's going on from a post. You could be lowering the rod tip from the target line, or the fly line is unrolling before you're generating enough power on your back cast, and your popper is falling. (Also, when the fly line unrolls the popper might be causing the line to snap a bit, like letting go of a stretched rubber band. This will add slack to the line and cause you to lose power on your cast.) Hitting the fly rod with the fly is something I struggled with, so my cures help you.
Techniques For The Long-Distance Fly Caster