Several times while posting a question (while clicking on the "Post your question" button) here on MSE I got weird behavior with the page. The browser asks me if I should leave the page or not to prevent losing some entered data instead of opening the page with recently published question:
In order to avoid losing my post I chose "Stay on Page" and pressed "Post your question" again. After that I saw the message that the post looks like a duplicate of an existing post:
That existing post is the question I just posted.
It seems that for some reason redirection to the posted question page occurs before the data is marked as saved.
My browser is Firefox 87.0 (64-bit) on Windows 10.