When creating a forum and selecting whole forum grading and then either rubric or marking guide and then selecting "save and return to course" it does not prompt to appoint to a rubric or marking guide, thus when you go to grade users you will see gray boxes and receive errors if you to navigate to each user. Selecting "save and display" will prompt you to finish setting up the forum grading.
Steps to replicate:
1: Go into a course and create a forum activity
2: Select whole forum grading and choose either Rubric or marking guide and you may use either scale or point. Add in a total grade (though not necessary)
3: Click "save and return to course"
4: The forum appears complete and you are back to the course page.
5: Login as a student user and submit a discussion to the forum you created.
6: Login as an admin or instructor now and click "grade users" You will see gray boxes: https://www.screencast.com/t/9LFjMnZwW6qA If you try to navigate to a different user errors will appear: https://www.screencast.com/t/ZUNtSN9u "Unable to save grade for Teacher Krista: Cannot read property 'elements' of null"
This is confusing for users because if you didn't know you needed to point a rubric or marking guide and just click to go back to the course thinking it was finished setting up and then later thinking you had an error.
To correct this after you have set up the forum and users have already replied, you can go back to the edit settings of the forum. Select simple direct grading and save and display. Then go back to the settings and click rubric and then save and display, this time you will be prompted to appoint your rubric. This will correct the grade users gray boxes.