This is probably because your web browser is improperly caching that old page. I would try using another web browser temporarily just to confirm that your tasks are still there. You can also try finding the tasks in that folder in a different way, like doing a search.
To fix your browser of choice, you may need to empty the cache, which varies depending on browser.
If you still think you are missing data, please create a support ticket and we'll try to help.