In cvshead, the edit settings page for a course (/course/edit.php), you can't change the value of "Availability." If you change it and save, it doesn't stick. You can change with the eye icon in the Add/Edit Category/Courses page.
The culprit seems to be in courses/lib.php on line 3561:
If you set something, it just reverts it. Changing it to !isset($data->visible).... seems to work, but I'm not sure what was intended here.