Using plugin format_topcoll 188.8.131.52 (2019052502) and Moodle 3.7.4+ (Build: 20200306).
When there are many columns and the last section is set to hidden, a student viewing the course page will see the layout changed to just one section. A teacher viewing the course page shows the correct number (multiple columns)
Steps to replicate:
1. Create a course.
2. Using Collapsed topic settings (course format):
Format: Collapsed topic
Number of sections: 7
Hidden sections: Hidden sections are completely invisible
Column orientation: Vertical
3. Save and go to the course contents page.
4. You should have the following layout:
col1 | col2 | col3
sec1 | sec4 | sec6
sec2 | sec5 | sec7
5. Turn editing on and click Edit Hide Section for sec7 (section7).
6. Log in as a student and visit the course.
Result: You will see that the layout is now just 1 column.