OK... for all of you following this thread. Yet another symptom.
Here is the gradebook setup. Moodle 3.0. There are 77 students, 204 gradebook items.
Today, I needed to clear an attempt for one of my groups on a quiz. Dang it...server tied up for 10 minutes! Students waiting and waiting all sitting in the classroom waiting for the attempt to clear so they could enter the quiz again.
But then...one by one, the students would say "I got in," ...and then another...One at a time their attempts cleared.
So I went to the page for the quiz. I repeatedly pushed the refresh button. First 20 attempts...then 15 seconds later, 19...and 15 seconds later 18. Keep hitting refresh and I could watch Moodle counting down until all attempts were cleared.
So my take on this. The gradebook is taking a long time in the way it is configured in MySQL to run the calcuations....and it is recalculating huge volumes of data...every student's final average, every affected assignment's averages, every folder or category and subcategory totals that are affected...recalculating dropping the lowest grades.