JMS序列化程序返回格式错误的JSON

Question

As title says, I have a problem with JMS serializer running on Symfony 2.7 which returns a malformed JSON. This happens only when database becomes bigger.

I made a simple function which returns the whole database serialized in JSON, sometimes is useful for me to check some data.

Basically I have this function

function asJson($serializationGroup = null)

{
    $serializer = SerializerBuilder::create()->build();

    $serGroups = array('Default');
    if (is_string($serializationGroup)) {
        $serGroups[] = $serializationGroup;
    }
    if (is_array($serializationGroup)) {
        foreach($serializationGroup as $sg) $serGroups[] = $sg;
    }

    $serializationContext = SerializationContext::create()->setGroups($serGroups);
    $serializationContext->setSerializeNull(true);
    return $serializer->serialize($this, 'json', $serializationContext);
}

which returns a JSON containing data associated to given serialization groups. Then I call it from a Controller giving all my serialization groups in order to serialize the entire db.

But, as I said, when my db becomes bigger I get a malformed JSON. Moreover the error is always different

SyntaxError: JSON.parse: expected ':' after property name in object at line 1 column 182085 of the JSON data

SyntaxError: JSON.parse: expected ',' or '}' after property value in object at line 1 column 367466 of the JSON data

SyntaxError: JSON.parse: expected ':' after property name in object at line 1 column 1158 of the JSON data

I tried to analyze the JSON and I noticed that it is totally corrupted after the error line.. Something like:

"commands_deletedse," <-- here starts the error, the rest is malformed
active ":true,"
readonly ":false,"
running ":false,"
...

---

UPDATE

It seems to work on another PC having MySQL 5.7 while the bug is present on another PC having MySQL 5.5. I don't know if it has something to do with..

---

UPDATE 2

It seems to work on the same PC but from Symfony command, hence I would say it has something to do with nginx configuration. In fact I even noticed that calling it from website works 1/10 time, so I would say the error comes from something like a timeout configuration or so. I use nginx + php-fpm.

---

UPDATE 3

I tried to starting the Symfony internal webserver and then call the controller function but I got the same error. I'm starting have no idea about what should I test..

Any thought?