Are you having trouble updating Assignment Grades or Feedback?
Your Grades have most likely been overridden in the Gradebook.
What happens if a grade has been updated in the gradebook it becomes locked. To unlock the grade you just need to:
Then go back to the Assignment and upload the feedback as normal.
As a default there is no override in Moodle. The Override only happens when grades have been entered manually into the Gradebook.
This commonly happens with grades and feedback have been uploaded directly to the Gradebook via a Spreadsheet.
NOTE: If you remove the Overriden grade then the score will revert back to the original grade for the Assignment. If you are just updating a feedback file, make note of the Grade listed in the Gradebook as you may need to re-apply this.