Images Missing from built in WP Gallery

You have a limit inside an script and you should change some values to adapt your needs:

jQuery....
//user settings
var thumbsPerPage = 15;
var maxPaginatedLinks = 200;
var hideEffect = "drop";
var showEffect = "drop";
var effectSpeed = "slow";
var count = 1;  
//handles multiple galleries on page
var galleryCount = $( "[id^=gallery-]" ).each( function()
var galleryId = "#" + $( this ).attr( "id" ) + " ";