Twister Skill Unbinding on Entering New Area

As the title says, every time I enter a new map or zone (including Abyssal Depths or my hideout) the Twister skill unbinds from my skill bar. This has only started happening since changing the offhand weapon in my second weapon set yesterday. I have died a few times after trying to use the skill only to find out it had unbound itself. Does anybody know how to fix this?