Replication steps:

1. Use Crio, open the Customizer and navigate to Design > Pages > Container and set to Full Width
2. Create a page and add a fixed width section (just container class, not container-fluid)
3. Add a table and toggle the setting for Responsive Table on tablet / phones
4. Preview the page and drag the screen in so it's phone view narrow
5. See the table has too much space on the sides:
   

If I uncheck flex here, it expands out as expected: