Hi,
I'm faced with a situation (Moodle 3.1.2+) where I activated quick grading to work around the issue with the grading interface crashing because of the unoconv problem, but the quick grading seems to be unavailable for some students. All I get is a mixed list of students where I can add a grade or mark for their submitted document and students where I can't add a grade or mark. The documentation is unclear why this is so.
Could it be that one of the teachers clicked the Grade button at some stage, which blocks the quick grading for that student?