You start to pull the rap rope, but can’t get it moving. Try a few tricks before you descend into utter despair.
You and your partner grab opposite ends of the ropes and pull, hard. One of you keeps the “pull” pressure on, while the other suddenly releases her end. The “rubber band” effect of one end of your dynamic rope “springing” upwards often will get a stubborn rope moving.
You can also do this with a Grigri or similar belay device. Crank as much tension as you can on the rope through the Grigri, and then pull hard on the handle to open it. The release in tension might be enough to free your rope. (This clever Grigri tip is from Andy Kirkpatrick.)