A person in the comments already mention that sometimes there is an error when using the addon alongside ElvUI with ElvUI throwing an error "does not exist!".
I have tracked down the issue, which is basically a race condition when loading addons. Both the ElvUI skinning handler for BetterWardrobe aswell as the OnEnable handler in Betterwardrobe get executed right when BetterWardrobe is loaded. Which one of the handlers gets executed first seems random and if the one from the ElvUI skinning handler is executed first, an error occurs as Betterwardrobe has not created its frames yet. I have found a pretty easy solution though which I will add as a merge request.

Pull request #160 fixes this issue.