This is a glitch that some users report once every few months, and fortunately, it's nothing to worry about. Your old tickets are always safe and sound, and your newly reported tickets will eventually arrive.
Visit Shake Status to see if everything is online. It's constantly monitored by our engineers and they will post all updates there.
What happens is that our servers can't service your requests at that exact moment. Everything usually gets back to normal within 10 minutes. Read more in this article.