There are two different types of saved progress for Free Code Camp: your profile and your browser cache.
Your completed challenges are all saved to your account in the FCC database. You can see the list of completed challenges and also the last submitted solutions by looking at your profile page.
Your progress tracking (map) is saved in your browser’s local storage. In-progress code is also saved in your local browser cache. If you are changing browsers or clearing your cache regularly you’ll have to use freecodecamp.com/map to navigate to your next challenge. Especially as you get to more complicated challenges that may take multiple sessions, I strongly recommend saving your in-progress work outside of the browser cache. This is a good opportunity to learn the ins and outs of your GitHub account, but you can also just save locally or use a service like repl.it which allows for versioning.
It sounds as though whatever automatic browser cleanup you have going on is resulting in you losing the cached data that tells the browser the last challenge you were on, but the cached solutions are still present. When this happens, just use the map to jump to your last challenge.