This was caused due to a security timeout. We're increasing the timeout and fixing the error handling for it.
What was happening is that the sessions were timing out for security reasons, and the error wasn't being handled properly.
The timeout is going to continue happening, but it will happen after 2 hours now instead, which hopefully will give everyone enough time to write amazing answers still, and if a timeout does happen, the website should handle it with a more useful error message.
We originally were going to timeout after 4 hours, but have decided to try out 2 hours first to keep the security down. Please let me know if you have this problem again!
If it does happen to you. Copy your answer and explanation, refresh the page and try again. And then let me know so I know that the timeout might not be long enough.