The Essential theme scalable background allows ddmarkers placed on an image during both the building process and the quiz operation to migrate to other screen areas depending on window scaling. This makes the quizzes essentially non-functional. May be related more widely to bootstrap issue. Sample images of problem are available at https://moodle.org/mod/forum/discuss.php?d=234375
To reproduce problem, use ddmarker plugin to create a quiz. Once created, with markers on screen, change window size. Markers will not align. Also can take quiz with window scaled to different sizes to see how scaling impacts answers.