Hmm. What Moodle version is it? I was just trying to replicate this on the Moodle Sandbox demo site and I am even unable to submit the assessment. I can have neither the assessment form using the "None" as a grade type, nor a point type with maximum grade set to 0. If I have such a form, the Workshop insists on a grade to be selected, even if there are no options to select from:
What I had to do was to set the second and all other aspects as point grades with maximum 1 point, but the weight set to 0. Then, the reviewer had a chance to submit the assessment and the grade got calculated correctly as 40 out of 70.
I agree this is not optimal and the workshop should allow for non-graded items be present on the accumulative assessment forms.
Still, I don't understand how your students are actually able to submit such an assessment form. Could it be that the assessment had been submitted before these extra aspects were added to the form?