Azure Function execution speed is extremely slow and inconsistent

I am writing few Azure Functions script that reads and write from/to an internal database and display relevant information into a webpage.

I noticed extreme slowness or even timeout in the web UI when loading the web page which calls the Azure Function script. After further investigation, I realized that the following:

1. Azure Function scripts sometimes takes anywhere between 10 seconds to more than 1 minutes to connect to SQL database.
2. Sometimes the scripts will run in few millisecond and sometimes it will take more than 3 minutes to completely run the script.

Here is my Azure Function script:

module.exports = function(context, req) {

context.log("Function Started: " + new Date());

// Import package
const sql = require('mssql');
var _ = require('underscore-node');
var moment = require('moment');
var Promise = require('promise');
// Create a configuration object for our Azure SQL connection parameters
var config = {
    server: "***", // Use your SQL server name
    database: "***", // Database to connect to
    user: "***", // Use your username
    password: "***", // Use your password
    port: ***,
    // Since we're on Windows Azure, we need to set the following options
    options: {
        encrypt: true
    },
    multipleStatements: true,
    parseJSON: true
};
var flagDefinitionId = null;

if (req.query.Id == null || req.query.Id == "" || req.query.Id.length == 0) {
    context.res = {
        // status: 200, /* Defaults to 200 */
        body: "No have flagDefinitionId "
    };
    context.done();
    // return;
}

var listTicketsFlag = [];

flagDefinitionId = req.query.Id;
sql.close();
var DBSchema = "b8akjsms2_st.";
sql.connect(config).then(function() {
    context.log("SQL Connected: " + new Date());

    var getAllEventTicketGoToMarket = new Promise(function(resolve, reject) {
        var queryGetEvent = ";WITH EventLog1 AS(" +
            " SELECT MD1, max([DateTime]) as LTime from " + DBSchema + "EventLog" +
            " where ([Event] = 'Ticket_Go_To_Market' OR [Event] = 'Acknowledge_Timeout')" +
            " group by MD1 )" +
            " SELECT * from ( SELECT EV.MD1 , EV.MD2," +
            " (SELECT COUNT(*) from " + DBSchema + "EventLog where MD1 = EV.MD1 and [Event] = 'Market_Ticket_Clear') as TotalClear" +
            " FROM " + DBSchema + "[Ticket] T" +
            " JOIN (SELECT E.* from " + DBSchema + "EventLog E join EventLog1 E1 on E.MD1 = E1.MD1 and E.[DateTime] = E1.LTime) EV ON T.Id = EV.MD1" +
            " WHERE T.IsInMarket = 1 and EV.MD2 <> ''" +
            " AND T.Id NOT IN (Select TicketId from " + DBSchema + "TicketFlag where FlagDefinitionId = " + flagDefinitionId + ")" +
            " ) R where R.TotalClear > 0";
        context.log("get event log - Ticket_Go_To_Market" + queryGetEvent);
        new sql.Request().query(queryGetEvent, (err, result) => {
            context.log("this is --------> EventLog " + result.recordset.length);
            resolve(result.recordset);
        });
    });

    Promise.all([getAllEventTicketGoToMarket]).then(function(values) {
        var ticketGoToMarket = values[0];
        context.log("this is --------> values: " + values[0].length + " ==+++++==== " + JSON.stringify(values[0], null, 2));

        if (ticketGoToMarket.length != 0) {
            listTicketsFlag = _.filter(ticketGoToMarket, function(num) {
                var countSP = num.MD2.split(',');
                // context.log("countSP =====> " + countSP.length + "num.TotalClear ==>" + num.TotalClear)
                if (num.TotalClear > countSP.length) {
                    return num.MD1;
                }
            });
            // context.log("listTicketsFlag =====> " + JSON.stringify(listTicketsFlag, null, 2));
        }
        insertTicketFlag();

    });

    function insertTicketFlag() {
        context.log("this is ----- ===> Insert:  " + listTicketsFlag);
        // insert
        var insertTicketFlagPromise = new Promise(function(resolve, reject) {

            context.log("listTicketFlag ----- ===> " + listTicketsFlag.length);

            if (listTicketsFlag.length == 0) {
                context.log(" -------------------- No have ticket need FLAG");
                resolve();

            } else {

                // insert new data to TicketFlag FlagTickets
                var listTicketInsert = ""; //convertArrayToSQLString(listTicketsFlag, true, flagDefinitionId);
                var len = listTicketsFlag.length - 1;
                for (var j = 0; j <= len; j++) {
                    listTicketInsert += '(\'' + listTicketsFlag[j] + '\', \'' + flagDefinitionId + '\')';
                    if (j != len) {
                        listTicketInsert += ",";
                    }
                }
                context.log("HERE : " + listTicketInsert);

                var insertQuery = 'Insert into  ' + DBSchema + '[TicketFlag] (TicketId, FlagDefinitionId) values ' + listTicketInsert + '';

                context.log("this is --------> InsertQuery" + insertQuery);

                // return;

                context.log("read data of FlagRule");
                new sql.Request().query(insertQuery, (err, result) => {
                    context.log("this is --------> insertQuery");
                    resolve(result);

                });
            }
        });

        Promise.all([insertTicketFlagPromise]).then(function(values) {
            context.log("DONE ALL");
            sql.close();
            context.done();
        })
    }

}).catch(function(err) {
    console.log(err);
    context.done();
});

};

How can resolve this slowness issue?