Debug wordpress website on mobile browser

I have a site [login to view URL] which is a wordpress site using a child theme on the OneEngine theme from EngineThemes ([login to view URL]) and when you open it in the default browser of several mobile phones (tried several), the preloader does not disappear. Everything works fine on desktop and Chrome for mobile, but it does not work in the default browser of mobile phones. The site seems to load under the preloader, can even scroll and everything, but the preloader does not disappear. I already tried reinstalling the parent theme, I tried changing back to the parent theme, but did not help. I also tried to install the theme to a test site and imported their demo data and that seemed to work. If there is a way, I would not like to build the site from ground up again. No idea where things went wrong. I need someone who can find the problem, fix it, and tell me what it was and how they fixed it.