There is a known bug in the rubric tool that potentially affects a student’s ability to view the feedback. Specifically, if the overall score is not selected, students will be unable to view the rubric feedback. The overall score is automatically selected once you select all the levels for each criterion, but if the rubric is closed too quickly, the overall score is sometimes not automatically selected and is left blank. As a workaround, be sure that all levels are checked and the overall score is selected before selecting Publish.
If your preferred method is to override the score for each criterion (entering in a score manually) the overall score will need to be manually selected before selecting Publish.