In order to see your hidden files in your timeline again, please follow the instructions below:
- In the menu select "Timeline".
- Press "View & Filter".
- In the side panel select "Hidden" and then close the panel
- Now you'll see all the hidden photos.
- If you want to show them again in your timeline, select them and then in the blue bar on the top of the page click "Show". All the photos you have selected are now visible on your timeline again.