Similar to https://github.com/bdaloukas/moodle-mod_game/issues/23

To recur:

1. (My site is in Moodle 3.5.3 currently.)
2. Create an activity in a course 'Game: Book with Question'.
3. There is no 'Turn editing on' button or any menu option under the activity page's gear icon.
4. The option 'Associate question categories to chapter of book' leads you to a blank page (see GitHub link above).
5. Press 'Attempt game' button to reach an error page.

(I'll add some screenshots of the error messages after I disable some of the other plugins, to make sure I only post directly related errors.)

I expected some kind of editing page, like for quizzes, books and lessons.