New grading screen does not completely load

We've just moved to Moodle 3.1 and have found that in some assignments the new grading screen does not fully load. See the screenshot for a visual example. it works in some assignments but not others. It may be related to the number of students. We do not have unoconv installed but ghostscript is installed and working fine. Digging in with debugging and firebug, it is definitely something from lib/ajax not loading fully. No errors are appearing in the web server logs, so I'm at a loss for where to look for further troubleshooting.