If you have lost progress in a course, it could be due to one of our commonly seen reasons:
You may have switched languages lately (from English to French, for example). When you switch languages in Codecademy, you can think of it as starting as a new user. Your progress hasn’t been lost—if you switch back to the language you started with, your progress will still be there. I know this is confusing, and we’re actively working on a solution to sort out this issue. I recommend sticking to one language so that your progress remains consistent. Also, you may want to go to Account --> Preferred Language and make sure your preferred/correct language is listed.
When a user creates an account with an email address then uses a third party authentication account (fb, google) to log in, and their authentication account is connected to a different email. Which means that they end up creating two accounts and the second account doesn’t have any of their progress.
-Codecademy Community Managers