I know that I have two activities in the General Section (Section 0), but when I switch to the Collapsible Topic, the course homepage shows "Section 0", and it is blank.
When I switch back to normal Topic format, I can see everything, including the activities under the General section.
The Moodle version is 3.9, and the theme is EduMy.
Here is the admin view of section 0 (General):
I reset the Collapsible Topic to default for every setting, but after entering the course, the first thing the user sees, is still Section 0 and it is still blank. See screenshot below: (The screenshot looks like it only has the header, because the content is shown as blank).