When trying to log in with cookies disabled, and entering the wrong username or password, the login prompt will say “Unknown error”.
Yes, it makes no sense, to try to log in with cookies disabled, but it can happen by mistake; the error message is remarkably unhelpful. (It looks like some kind of CSRF failure, so probably it should just say that.
This is such a rare and self inflicted problem that I am not sure any engineering time is warranted.
A pull request to improve the error message is welcome 
I’m getting this too. Extremely annoying. I’m on a pixelbook.
Hello,
I too believe that error messages should be more clear and point towards a solution. Moreover, the fix is pretty easy and I believe some users will love it!
Here is the pull request I made. This is what it looks after:
I am not too sure about the wording and if you have any suggestions, I greatly appreciate them.
Merged this in, thanks for the fix! 
