can't add new questions after creating a new quiz?

Please tell me what other plugins and theme you are using because we are not having any such issue both in our testing environment and on production . You can check demo at https://www.wpcues.com/wpcuesbasicquiz/wp-admin yourself.

We checked both the problems on other production environments. It occurs rarely (say 0.1%). The problem occurs because quicktags required for wp_editor does not get loaded correctly. So, to rectify it , just try to refresh and try to add question again.

are you still having this issue?