No trend chart at all neither on the Job Page and nor in previous builds.
It might worth to mention that we are developing a tool based on trends of legacy code, so this might be different scenario that usual (e.g. we are not working on the HEAD commit and we rerun the same commit many times).
But you can see results in the details page of every job?
Which browser are you using? Do you have a reverse proxy installed? Can you open the developer perspective in your browser and have a look if there are any errors popping up?
Do you see the elements in the Issues tab, they are also loaded using AJAX? How is your Jenkins instance protected? Are you using a reverse proxy? When there is a 500 error, then Jenkins should also report something in the log file, can you please check?