Styles are duplicated when compiling LESS to CSS. How can this be fixed?

Question

css

I compile the project with Galpom, I write styles through LESS and when compiling LESS files into one common.min.css file, all styles are repeated 2 times, how can I fix this?
,
here is the task:

gulp.task('less', function () {
  return gulp.src('./app/less/**/*.less')
  .pipe(less())
  .pipe(concat('common.css'))
  .pipe(cleanCSS())  
  .pipe(rename({suffix: ".min"}))
  .pipe(gulp.dest('./app/css/'));
});

and imports: