Why does an OpenSSL error occur when using curl?

Question

PHP

I send notifications using multi curl and firebase cloud messaging service. All messages with different data, so one message, specifying only tokens, cannot be sent. (Probably not the best solution) When sending about 400 messages, everything is OK, if more (eg 800) then an OpenSSL error occurs. Ubuntu 18.04 system, updated openssl to 1.1.1b, did not help. At the same time, I checked it on another server with the same OS versions, openssl, curl, php, everything worked there.
OpenSSL SSL_connect: SSL_ERROR_SYSCALL in connection to fcm.googleapis.com:443

$connectionArray = [];
$cmh = curl_multi_init();

$headers = [
    'Authorization:key = fcm.serverKey',
    'Content-Type: application/json'
];

foreach($notifyArr as $notify) {
    $fields = [
        'registration_ids' => explode(',', $notify->user_token),
        'priority' => 'high',
        'content_available' => true,
        'notification' => [
            'title' => $notify->title,
            'body' => $notify->text,
            'sound' => 'default'
        ]
    ];

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, 'fcm.url');
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
    curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 10);
    curl_setopt($ch, CURLOPT_TIMEOUT, 10);
    $connectionArray[] = $ch;
    curl_multi_add_handle($cmh, $ch);
}

$running = null;
do {
    curl_multi_exec($cmh, $running);
} while($running > 0);

foreach($connectionArray as $ch) {
    $info = curl_getinfo($ch);
    if( $info['total_time'] <= 0 || !is_numeric($info['total_time']) ) {
        $errors = true;
        continue;
    }
    curl_multi_remove_handle($cmh, $ch);
}
curl_multi_close($cmh);

Answer 1

In general, for those who are interested, I broke $notifyArr into arrays of 100 elements, the error disappeared