We have come across the same issue while using X-theme with Cornerstone front end editor. The save takes up to 10 seconds longer while API Services are enabled.
this is the closest question about navception i could find so i thought i would add it here.
Navception breaks the new wordpress customizer but if you add this it gets around the bug
navception.php line 102
// Don't navcpetion in the customizer
global $wp_customize;
if (isset($wp_customize)) {
return $items;
}
