If the instructor publishes a quiz and sends it to the gradebook, then deletes the quiz after it has submissions, restoring the quiz recreates the GB column but does not send existing scores to the GB. A message (and a help article) are needed so instructors are aware that they need to take extra steps to send existing scores to the GB again.

Thanks to Tiffany for the proposed text:

Note: After restoring a published assessment with Send assessment score to Gradebook immediately on submission enabled in its Settings, grades may not reappear in the Gradebook automatically. Follow the steps in [link help article here] to restore the grades to the Gradebook.

And then have a linked help article walking through editing the settings, unchecking the box and saving, then editing again to recheck the box and save.