I was on https://stackexchange.com/newsletters and tried to preview the Android Enthusiasts newsletter, and the pop-up contained the Oops! Something Bad Happened! page.
I tried for StackOverflow, of which I'm a member, and it worked fine (I had already previewed that newsletter from StackOverflow itself) but then I tried English Language and Usage, of which I'm also a member, and it did not work. I then went directly to the English page, and tried there, but it still crashed.
Finally, I tried it logged out, and in both Firefox and Chrome, and in all cases StackOverflow preview worked but the others did not.