Uglifyjs duplicate files?

Question

JavaScript

gulp.task('build', function () {
return gulp.src('app/html/*.html')
.pipe(useref())
.pipe(gulpif('*.js', uglify()))
.pipe(gulpif('*.css', cssnano()))
.pipe(gulp.dest('dist'));
});
the code is correct, but for some
reason a double occurs, it writes the same script 2 times into two different files (once in each)
At the same time, some files do not press at all