Theme twig files front page is empty
You have two problem. 


page--front.html.twig is special suggestion template for front page. Any url set to front page always use this template => You don't need set alias for this.Just set page you want to front page.
Don't add html tag to page template. The tree of template is html=>page=>region=>block... Html tag exited in template html.html.twig. 


And more you can setting twig debug to see current home page use template?