We store your solutions in your browser's local storage. So if you're using a different device, or browser, or if you cleared your browser's local storage for some reason, these will not automatically appear when you visit a challenge. Instead, you will need to access them from your code portfolio.
Click your photo in the upper right hand corner of FreeCodeCamp.com and you will see your code portfolio. Scroll down and you should see your solutions. If you click one, you will then see the challenge with your solution loaded in from our database.
Please let me know if I can be of further help with this.