Elise's Rappel Doesn't Activate Sometimes

It has happened many times in the past where I would be trying to escape and press E to rappel to buy some extra time and it wouldn't let me. When this happens I have to click on a monster or enemy in order for it to go off. It doesn't happen all the time, but it happens enough to be annoying. I have it set on quick cast maybe that has something to do it but I'm still not sure. Anyone else experiencing this? Or Is it just me?