Overnight, my students' grades all dropped 20% or more. I checked all assignment settings to make sure the boxes are not selected that would count each ungraded assignment as a zero or require passing scores before credit being given. I checked the weight and calculation percentages of each assignment, and all seem to be in order. I even made sure every assignment for a top student was graded, and despite having many scores of 100% and the lowest score being 86%, this overall grade is being calculated at a 65%. Is there any reason or any setting I might be missing that might cause this, or perhaps a way to completely reset my grade book to fix this issue?