Form not displaying on the mobile version of an website.

On this website there is a form that is usually visible but not when using the mobile version: http://www.osrportal.eu/en/repository/search/pdasearch

I'm talking about <form id="views-filters" method="get" accept-charset="UTF-8" action="http://www.osrportal.eu/en/repository/searchact">

Can someone explain why it is hidden in the mobile version?