Flat Responsive was updated to version 1.0.3 with a few bug fixes. You can check the changes here.
Changes Made
1. Fixed The Customizer Bug
2. Menu Font Size Customizer Added
NOTE: A reminder that if you made any changes to the theme’s files, including the style.css file, these will be overwritten. It’s also recommended you make a copy of your theme and save it somewhere as a backup.