There are a couple of solutions that may resolve a blank search results page...
1.) Change the setting under Flexmls IDX > Settings > Behavior - Multiple Summary Lists
Allow multiple lists per page
2.) Re-save your Permalink settings under Settings > Permalink. You won't need to change anything on this page, just click Save Changes on the bottom of the page.
3.) The Search page that is created upon activation of our plugin may have been deleted