Based on another bug report, I am going to guess that you have a noscript feature enabled, and you chose to ignore the large noscript warning at the top warning you that the site is going to break in a bunch of ways if you don't enable JS.
We've fixed the blanking of collapse regions with noscript... we think. So it should at least be visible. But you should know you're going to run into other errors because JS-less is not supported and is hiding an ever-increasing fraction of the site from you, between annotations & transcludes.
Never seen anything like this.