We have a problem where the drop down to display Submission comments in the gradebook won't work for one or more random assignment: it just bring the browser at the page top instead of displaying the ajax loader. Refreshing the page change which assignment having the problem.

I found out that the problematic comments get the same id as its predecessor, so based on Damyon comment in https://tracker.moodle.org/browse/MDL-40096, I edited \comment\lib.php and changed the call from uniqid() to html_writer:random_id() in the constructor. So far so good, it seem to have resolved the problem.

    public function __construct(stdClass $options) {

        $this->viewcap = false;

        $this->postcap = false;

        // setup client_id

        if (!empty($options->client_id)) {

            $this->cid = $options->client_id;

        } else {

            $this->cid = html_writer::random_id(); //uniqid(); <-- change here

        }

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