Alter the shortcode logic to be AND instead of OR

functions.php

/* Tribe, change tax query relation to AND instead of OR */
function tribe_list_widget_tax_query_relation ( $args ) {

    // bail if no relation is no tax query
    if ( !isset( $args['tax_query'] ) ) return $args;

    $args['tax_query']['relation'] = 'AND';

    return $args;
}
add_filter ( 'tribe_events_list_widget_query_args', 'tribe_list_widget_tax_query_relation', 100 );