By using your same mobile devices, please also browse our official DEMO and see if you are experiencing the same problem. If the same issues happen in our DEMO as well, this means, our template would need to be updated to solve those errors. (hiding the text from the slider doesn't sound a problem to me. I guess it has been done that way on purpose to avoid the mess)
For further modification for the responsive layout you should be doing some changes to this file:
/templates/flexible_lightmart/css/responsive.css
Regards.