WAB Developer 2.19
Still dealing with caching of a deployed Web AppBuilder app anytime changes are made and is redeployed. THIS thread actually solved the main problem, however it only solves it if the url is navigated to from a regular browser window. Unfortunately, the way this particular WAB app is opened (a link on another non-ESRI web application) is navigated to as a popup window. From what I know, the developers are navigating to this WAB via window.open()
While the cached version is dealt with, I think the index.html conatains css that causes the window to look broken.