It could be because you have opening tags that are not closed. I put your code in to the checker and it complained about the body element being found before the div is closed:
<body><div class="container"> <!-- no closing tag for this div --><header><h1>Header</h1></header><hr><p> TEXT </p><div><hr><footer>Footer</footer></div> </body>Message filteringInfo: The Content-Type was text/html. Using the HTML parser.Info: Using the schema for HTML with SVG 1.1, MathML 3.0, RDFa 1.1, and ITS 2.0 support.Error: End tag for body seen, but there were unclosed elements.From line 27, column 1; to line 27, column 7Error: Unclosed element div.From line 17, column 1; to line 17, column 23
Fix that and rerun the tests.