function getOrdersByUserId(userId, month = 4) {
    const apiService = new ApiService();

    return apiService.getOrdersList(`?OrderingUser=${userId}`)
        .then(orders => {
            const monthOrders = orders.filter(order => new Date(order.FromTime)
            .getMonth() === month);

            return monthOrders;
        });
}

getOrdersList(queryString = '') {
    return httpsRequest.createRequest(this.URL.ordersList + queryString, {}, this.requestHeaders, 'GET')
        .then(result => JSON.parse(result).Records);
}

const promises = userIds.map(userId => {
            return getOrdersByUserId(userId, month)
                .then(orders => {
                    return orders;
                });
        });

        Promise.all(promises).then(results => {
            console.log(results);
        }).catch(err => {
           console.log(err);
        });

(node:1) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): SyntaxError: Unexpected end of JSON input

const results =
    userIds.reduce((acc, userId, index) => {
        acc.p =
            p.then(getOrdersByUserId(userId, month))
             .then(orders => {
                 return acc.results[index] = orders;
             });
        return acc;
    }, {p: Promise.resolve(), results: []})
    .then(acc => acc.results)
    .then(results => {
        // `results` is an array of results, in the same order as `userIds`
    })
    .catch(err => {
       console.log(err);
    });