You may need to relink (re-upload) local files you previously added in the following situations. Once the relinking is completed, all related edits will be restored automatically.
For Premium users:
The files failed to sync successfully with your Cloud Space;
The files have been removed from your Cloud Space.
For Free users:
You are using a different browser;
You are using a different computer;
You are using a new Incognito/Private window;
The files have been removed from your local device.
Also read: How to relink missing files?