Nodejs is disconnected from Rainbow platform

Hi , I have developed a Nodejs application with version  2.25.2-lts.11

I noticed some times that the rainbowSDK.events.on('rainbow_ondisconnected' is called 

In this case the application cannot receive or send any Instant Message.

The options in my application are:

let options = {
    "rainbow": {
        "host": "sandbox.openrainbow.com"
    },
    "credentials": {
        "login": USER_NAME,// To replace by your developer credendials
        "password": PASSWORD// To replace by your developer credentials
    },
    // Application identifier
    "application": {
        "appID": appID,
        "appSecret": appSecret
    },
    // Logs options
    "logs": {
        "enableConsoleLogs": true,
        "enableFileLogs": true,
        "color": true,
        "level": 'debug',
        "customLabel": "mxar",
        "system-dev": {
            "internals": false,
            "http": false,
        },
        "file": {
            "path": "/var/tmp/rainbowsdk/",
            "customFileName": "R-SDK-Node-Sample2",
           // "level": "debug",
            "zippedArchive" : false,
           /* maxSize : '10m',
            maxFiles : 10 */
        }
    },
    // IM options
    "im": {
        "sendReadReceipt": true,
        "messageMaxLength": 14024, // the maximum size of IM messages sent.
        "sendMessageToConnectedUser": false, // When it is setted to false it forbid to send message to the connected user. This avoid a bot to auto send messages.
        "conversationsRetrievedFormat": "small", // It allows to set the quantity of datas retrieved when SDK get conversations from server. Value can be "small" of "full"
        "storeMessages": false, // Define a server side behaviour with the messages sent. When true, the messages are stored, else messages are only available on the fly. They can not be retrieved later.
        "nbMaxConversations": 15, // parameter to set the maximum number of conversations to keep (defaut value to 15). Old ones are removed from XMPP server. They are not destroyed. The can be activated again with a send to the conversation again.
        "rateLimitPerHour": 900000, // was 10000 Set the maximum count of stanza messages of type `message` sent during one hour. The counter is started at startup, and reseted every hour.
        //"messagesDataStore": RainbowSDK.DataStoreType.StoreTwinSide
    },
    "requestsRate": {
       "useRequestRateLimiter": true,
       "maxReqByIntervalForRequestRate": 20250, // nb requests during the interval.
       "intervalForRequestRate": 60, // nb of seconds used for the calcul of the rate limit.
       "timeoutRequestForRequestRate": 600, // nb seconds Request stay in queue before being rejected if queue is full.
    },
    "xmpp":{
      "maxIdleTimer": 50000
    }
};

Why the nodeJS application is disconnected?
How can I connect again?

Thanks in advance

Marios