Use get_post_types to query only custom posts types

Instead of creating a string try creating an array and check.

$posttypes_array = array();
foreach ($post_types  as $post_type ) {
    $posttypes_array[] = $post_type;
}

And then form the query as follows

$buildArgsAllQuestions = array( // Add out new query parameters
    'post_type' => $posttypes_array,
    //'post_type' => $posttypes_array,
    'orderby' => 'date',
    'order' => 'DESC',
);