For some reason, FacetWP doesn’t support infinite scroll when paired with the Posts module in Beaver Builder. However, working with some code from GitHub, I was able to modify it to work with Beaver Builder. Here is the code:

(function( $ ) {
    'use-strict';
    var throttleTimer = null;
    var throttleDelay = 100;

    $(function() {
        var $win = $( window );
        var $doc = $( document );

        function FWPCustomInfiniteScroll() {
            clearTimeout( throttleTimer );
            throttleTimer = setTimeout(function() {
                if ( $win.scrollTop() !== $doc.height() - $win.height() ) {
                    return;
                }

                if ( FWP.settings.pager.page < FWP.settings.pager.total_pages ) {
                    if ( ! $( ".facetwp-loading-placeholder" ).length ) {
                        $('<p class="facetwp-loading-placeholder">Loading...</p>').hide().appendTo('.fl-module-post-grid').fadeIn(500);
                    }

                    FWP.paged = parseInt( FWP.settings.pager.page ) + 1;
                    FWP.is_load_more = true;
                    FWP.soft_refresh = false;
                    FWP.refresh();
                }
            }, throttleDelay );
        }

        $doc.on( 'facetwp-loaded', function() {
            $('.fl-module-post-grid .facetwp-loading-placeholder').remove();
            if ( ! FWP.loaded ) {
                $win.off( 'scroll', FWPCustomInfiniteScroll ).on( 'scroll', FWPCustomInfiniteScroll );
            }
        });
    });
})( jQuery );

If just want to play around with the code without modifying files on the server, try out the Additional JS plugin that lets you load just Javascript directly in the customizer.