I was running into a problem where answers were not being saved when I was creating questions, resulting in all answers being marked as incorrect. I searched the support forums and found others sporadically had the same problem, with no clear cut answer as to why this was happening.
I pulled up my js console and saw that 'tinymce' was not defined (resulting in a reference error on line 35 of the wpproquiz.admin.min.js when I was saving the answers.
This is because (and I imagine it is similar for others) I had disabled the visual editor from my profile page within the wordpress dashboard, resulting in tinymce not being loaded. Re-enabling "visual editor" fixed the problem and allowed answers to be saved.
This is a less than ideal fix as I need visual editor disabled for other aspects of my site. A permanent fix for this plugin, I imagine, would be load the necessary visual editor modules for the plugin if the visual editor is disabled.
I paraphrased a lot of the errors here, so if you need more specific info let me know though I imagine you can recreate the problem by disabling visual editor from your profile page and then trying to create some questions and save some correct answers.