When we deploy new functionality or bug fixes in the Fatpaint-backend, the servers need to be restarted. The editor should automaticaly recover from this, but we noticed that for some Guest users, it is not working. So we recommend people to sign-up.
On the next release of the editor, we will implement a messaging system so that users are alerted before we restart the servers, so that users get a chance to save projects and so on.