Hello,
The field group looks corrupted, the fields property in the JSON file is empty. I also import the JSON file to my demo site and do not see any fields. You can try to re-create the fields with the same IDs to continue managing them.
How would this be possible ?
I'm not sure. But there is a case that you click on the Update button in the field group, while the fields are loading and not displayed and you click on the Update button again, all fields will lost.
is there a way to regenerate from the database setup?
If you have a backup file from the point before the issue occurs, you can try to restore it.
.
