In my case the error was presented when using the "tabs" format. However, I managed to solve it.
What I did was put the course in "topics" or "weeks" format and select a section that was not empty and put it in "highlight" (I use Moodle in Spanish so I do not know how you put it in English), after that I put it back in the "tabs" format and it was working. I did this many times and yes, that was the error in my case.
I think a kind of bug is generated when Moodle sees empty sections, there may be the core of the problem.