Hi Rob,

I've not been able to reproduce this. Did this affect only one course? Changing visibility of sections requires the capability 'moodle/course:sectionvisibility' in the course context, you should check if editing teachers and admins have that capability in your system.

Also maybe have a look at the visibility settings of each activity/resource in the section. Maybe the system is somehow trying to toggle a hidden section with visible modules, and so is then setting the section to visible but hiding the modules?