If you leave the Digidentity webpage open and inactive for fifteen minutes, you will see a notification warning that the session is about to expire. If you respond in time, you can choose to stay logged in. If not, you will be automatically logged out.
This session timeout is in place for security reasons. It prevents others from accessing your information if you leave your device unattended. Any details you have entered up to that point will be saved.
For steps on how to return to your registration, please see the following article: How do I return to my registration?