Which theme are you using? I believe a lot aren’t compatible with Mendix 8.
The error is referring to some configurations that seem to be missing, which could be due to an incompatible theme. Normally your index.html should look along the lines of
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<title>Mendix</title>
<meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1, maximum-scale=1">
<meta name="apple-mobile-web-app-capable" content="yes">
{{themecss}}
<!-- ICONS EXAMPLE -->
<!-- iPhone retina icon (iOS < 7) -->
<!-- <link href="resources/ios/icons/apple-touch-icon-precomposed-114x114.png" sizes="114x114" rel="apple-touch-icon-precomposed"> -->
<!-- STARTUP IMAGES -->
<!-- <link href="resources/ios/startup/apple-touch-startup-image-1496x2048.png" media="(device-width: 768px) and (device-height: 1024px) and (-webkit-device-pixel-ratio: 2) and (orientation: landscape)" rel="apple-touch-startup-image"> -->
</head>
<body dir="ltr">
<div id="content"></div>
<script>
dojoConfig = {
baseUrl: "mxclientsystem/dojo/",
cacheBust: "{{cachebust}}",
rtlRedirect: "index-rtl.html"
};
</script>
<script>
if (!document.cookie || !document.cookie.match(/(^|;)originURI=/gi))
document.cookie = "originURI=/login.html";
</script>
<script src="mxclientsystem/mxui/mxui.js?{{cachebust}}"></script>
</body>
</html>