by Ken Task.
Follow up after testing with a 3.3 and a 3.2 ...
When editing a section, one has an option to use custom ... which means Moodle won't auto generate 'Topic 1', 'Topic 2', etc. but, rather, whatever the user inserts. The box for the Section Title won't accept HTML ... even if one manually inserts it (like <b> some text </b>). But there is also a 'Summary' one can use under the Section Title that does allow HTML.
One might need to query the database to see what's in both of those objects:
select * from `mdl_course_sections` where `course` like "12"
The 12 in the example above is the ID of the course.
The output of that will show the attributes of all sections in course ID - both the Section Name and the Summary. The Summary, if used and if teacher/editor used the HTML editor for the Summary, could have errant HTML tags that might be involved.
'spirit of sharing', Ken