SDK locking up when inside a forked process

#!/usr/bin/php

<?php

include __DIR__ . '/application/cli/environment.php'; // basically composer autoload 

use \Couchbase\ClusterOptions;

use \Couchbase\Cluster;

$username         = 'username';

$password         = 'password';

$connectionString = 'couchbase://10.10.10.10';

$clusterOpts = new ClusterOptions();

$clusterOpts->credentials($username, $password);

$couchbase  = new Cluster($connectionString, $clusterOpts);

$bucket     = $couchbase->bucket('default');

$collection = $bucket->defaultCollection();

$result = $collection->upsert('test-key', [time(), 'some data']);

$data = $collection->get('test-key')->content();

print_r($data);

$processId = pcntl_fork();

if ($processId < 0) {

    // cleanup using posix_kill & pcntl_wait

    throw new RuntimeException('pcntl_fork failed.');

} elseif ($processId === 0) {

    // WE ARE IN THE CHILD

    $clusterOpts = new ClusterOptions();

    $clusterOpts->credentials($username, $password);

    $couchbase  = new Cluster($connectionString, $clusterOpts);

    $bucket     = $couchbase->bucket('default');

    $collection = $bucket->defaultCollection();

    $data = $collection->get('test-key')->content(); // <-- locks up and never returns

    print_r($data);

} else {

    // WE ARE IN THE PARENT

    echo "parent\r\n";

}