Just wait for about 15 minutes and restart your device. If you're talking about this website then it's just pretty common for your reply, comment to disappear. It'll reappear in a few minutes and the logging in or out problem is because of a system error.
I'm not sure what is going on but no matter what browser: Firefox, Chrome, IE, I cannot comment either logged in or out.
Just wait for about 15 minutes and restart your device. If you're talking about this website then it's just pretty common for your reply, comment to disappear. It'll reappear in a few minutes and the logging in or out problem is because of a system error.