I have a few questions that might help identify what has happened:
Did you login to the Machine Learning for Kids website on the second day?
Did you use the same web browser on the same computer both times?
Were you using an "Incognito" or "Private Browsing" mode?
Is there any chance your browser storage was cleared, such as by using "Delete browsing data" or "Clear history" after the first day?
Kind regards
D