I have just upgraded to version 4 and the menu is not working on mobile devices, however it is ok on tablets and desktop. I am not using a child theme, however I have a small amount of custom css as detailed below. The website is here http://www.malonecleaningservices.co.uk, Do I need a new style/css and functions.php file as kanashi?
.container {
margin: 0 auto;
max-width: 10388px;
}
#access ul { margin:0px 0px 0px 33px; }
.entry-header { display: none;}
.entry-title { display: none;}
#main { padding: 0px 0 10px 0px; }
.entry-content {margin-top:0px;}
#site-generator { display : none; }
.hgroup-wrap {display:none;}
header img {margin:20px 0px 0px 0px; }