Field collection fields are empty in edit mode
I've experienced this a while ago with field collections and paragraphs but can't remember the exact cause.  Suggestions for troubleshooting:


Check to make sure there's no updates available for the field collection module, Drupal Core, or any other modules that may be impacting the types of fields you're trying to assign in your field collection.
If your field collection involves an entity reference to either:


another node and allows creation of said node within the edit form, make sure to click save on the embedded node creation form before saving the overarching node.
a file upload, make sure to upload the file before clicking save on the overarching node.



If this still doesn't work, try creating the field collection from scratch, adding one field at a time to determine which one is causing the issue.