You need to add a text to the questions in order to for the mainEntity to appear. To avoid this in the future, just set a minimum amount of question body length greater than zero. Regarding existing questions with no content you will have to manually update them and add relevant content.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask here, in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.
April 20, 2021: Q2A 1.8.6 released!