If you take too long to post a comment, my experience is that the link may expire and I get that same error message. Save or copy your contents, refresh the screen to create a new link, paste your copied content and hit submit. Works every time for me.
I did that a bunch of times. Also cleared browser data. Haven't tried in a while, but I'm over it for now anyway
Sometimes I use preview and then post and it works. Or copy what you wrote and start fresh. I have had that a few times.
(post is archived)