grunt uglify is missing files

I'm looking at upgrading Drupal version of jQuery UI but since 1.12 and the folder change of some effects and widgets, the uglify tasks is missing a lot of files, everything that is in widgets/* and effects/* essentially. We're using the individual files so this is preventing up from upgrading (for reference: https://www.drupal.org/node/2533498)

$ grunt uglify
Running "uglify:main" (uglify) task
>> Destination dist/jquery-ui.min.js not written because src files were empty.
>> No files created.

Running "uglify:i18n" (uglify) task
>> Destination dist/i18n/jquery-ui-i18n.min.js not written because src files were empty.
>> No files created.

Running "uglify:ui/core.js" (uglify) task
>> 1 file created.

Running "uglify:ui/widget.js" (uglify) task
>> 1 file created.

Running "uglify:ui/mouse.js" (uglify) task
>> Destination dist/minified/mouse.js not written because src files were empty.
>> No files created.

Running "uglify:ui/draggable.js" (uglify) task
>> Destination dist/minified/draggable.js not written because src files were empty.
>> No files created.

Running "uglify:ui/droppable.js" (uglify) task
>> Destination dist/minified/droppable.js not written because src files were empty.
>> No files created.

Running "uglify:ui/resizable.js" (uglify) task
>> Destination dist/minified/resizable.js not written because src files were empty.
>> No files created.

Running "uglify:ui/selectable.js" (uglify) task
>> Destination dist/minified/selectable.js not written because src files were empty.
>> No files created.

Running "uglify:ui/sortable.js" (uglify) task
>> Destination dist/minified/sortable.js not written because src files were empty.
>> No files created.

By tweaking the Gruntfile.js I was able to get the rest of it by adding this to the minify object (but then there are leftover js files in dist) :

dynamic_mappings: {
	files: [
		{
			expand: true,
			cwd: 'ui/',
			src: ['**/*.js'],
			dest: 'dist/minified',
			ext: '.min.js'
		}
	],
	options: {
		banner: createBanner()
	}
}