I've been getting 502 errors when saving certain projects in the WordPress admin. After digging into the nginx error logs I traced the issue to a PHP warning cascade in wp-content/themes/lay/updatejson/update_thumbnails.php, lines 428–444:

PHP Warning: Trying to access array offset on int in update_thumbnails.php on line 428
PHP Warning: Trying to access array offset on int in update_thumbnails.php on line 429
... (repeats for every line in the unpack block)

The warnings flood the FastCGI response headers until nginx rejects the response with a 502.

Bug cause

update_thumbnail_in_json_recursive() accepts a single $thumb_data array as its third parameter. However, the stack branch calls it passing individual positional arguments instead:

else if ($array[$i]['type'] == 'stack' ) {
    LayUpdateThumbnails::update_thumbnail_in_json_recursive(
        $array[$i]['cont'], $needsUpdate, $post_id, $permalink, $title,
        $featuredImgId, $featuredImgUrl, $ar, $sizesArr, ...
    );
}

This means $thumb_data receives the value of $post_id (an integer) inside the recursive call. When the function then tries to unpack $thumb_data['post_id'], $thumb_data['permalink'], etc., PHP fires a warning on every single line of the unpack block.

For reference, the carousel and elementgrid branches in the same function call it correctly:

else if ($array[$i]['type'] == 'carousel') {
    LayUpdateThumbnails::update_thumbnail_in_json_recursive(
        $array[$i]['carousel'], $needsUpdate, $thumb_data
    );
}

Hope this helps. Happy to provide any additional info if needed.