How is the off canvas setup I see something going on in my tests here on your site the following code is added just above the closing body tag when the menu button is pressed to display your off canvas backdrop
<div class="modal-backdrop fade show"></div>
But on my test when I just uploaded a quick canvas page and hit a button I get this for the backdrop
<div class="offcanvas-backdrop fade show"></div>
Also if I edit the class on your site the menu then becomes at the front and works as intended