The following just happened to me (on softwarerecs, but I guess it should be the same for all SE sites):
- I was entering a new question.
- When trying to post it, I was asked to solve a CAPTCHA. (*)
- I allowed JS from google.com, which required a reload of the page.
- After the reload, my question content was lost.
(* Probably because I had the question form open for many hours.)