WP-Query not returning all results

Question

I want to return all parent events from the posts-table (where post_parent = 0).

This works absolutely fine when I run a raw sql query but when I run a wp_query in my PHP class I will only receive 8 rows from the WP's posts-table. I turned cache off and tried other things but I can't get my head around why not all 23 rows are returned by the WP query. Thanks for any hint.

Raw SQL Query (works fine - 23 rows):

select * from wp_posts 
where post_type = 'tribe_events' and post_parent = 0 and post_status = 'publish';

WP Query (only returns 8 rows which is wrong)

$args = array(
        'post_type' => 'tribe_events',
        'posts_per_page' => -1,
        'post_status' => 'publish',
        'post_parent' => 0
);
$evts = new WP_Query($args);

Answer 1

There are two things I would try to understand the cause of your problem.

(1.) Use 'suppress_filters' = true to insure that no filters are modifying your query.

$args = array(
    'post_type' => 'tribe_events',
    'posts_per_page' => -1,
    'post_status' => 'publish',
    'post_parent' => 0,
    'suppress_filters' => true
);
$evts = new WP_Query($args);

(2.) Dump the actual MySQL query that WordPress is using by using the filter 'posts_request'.

add_filter( 'posts_request', function( $sql ) {
    error_log( 'SQL=' . $sql );
    return $sql;
} );

Of course, for this filter to work 'suppress_filters' must be false.