Drupal 8, populates the Search API queue for indexing all entities. Needed in cases where the entity does not populate the index queue on its own.

Search API Reindex

<?php

$index = \Drupal\search_api\Entity\Index::load('index_name');
foreach ($index->getDatasources() as $id => $datasource) {
  $index->trackItemsInserted($id, $datasource->getItemIds());
}