Postgresql – Can not res.send() (error: "Cannot set headers after they are sent to the client") after I do query to database PostgrSQL

I know, it sounds really wierd, but it’s true.
I was sitting and making an API on node.js, but when I began to test it, I was surprised to find out that nearly in beginning of query treatment when the first res.status().send() reached, VS Code drop a "Cannot set headers after they are sent to the client" error.
How I realize that database query is guilty? I used "res.finished" property to check out when it "sent to client" and discovered that res.finished changes from "false" to "true" exactly after db query.

Who knows what it can be? I had done the same API thing with MySQL database and it went nice, but now I’m using PostgreSQL, so things start to happen.

I export "PostgreSQL manager" class from typescript file

PostgreSQL_Manager.ts:

module.exports = {
    PostgreSQL_db_manager    
}

Import and initialize it in index.ts:

index.ts

const PostgreSQL_mngr = require('./PostgreSQL_Manager.ts').PostgreSQL_db_manager;
const db = new PostgreSQL_mngr;

And then, if I comment the statement with query to database, res.finished stay false (I tried it with readRows (SELECT) and with createRows(INSERT INTO)):

Piece of index.ts code: 

console.log('res.finished : ', res.finished);
//let nickval : any = await db.readRows('users', 'nickname', `nickname = '${nickname}'`);
//await db.createRows('test', '(color, odor, taste, quantity)', '('meaningless', 'absent', 'sadness', 0)');
console.log('res.finished : ', res.finished);

Piece of Terminal:

res.finished :  false
res.finished :  false

But when I uncomment database query, it becomes this:

Piece of index.ts code: 

console.log('res.finished : ', res.finished);
//let nickval : any = await db.readRows('users', 'nickname', `nickname = '${nickname}'`);
await db.createRows('test', '(color, odor, taste, quantity)', '('meaningless', 'absent', 'sadness', 0)');
console.log('res.finished : ', res.finished);

Piece of Terminal:

res.finished :  false
Postgres: Rows were created...
res.finished :  true

Code of db.createRows in postgres manager class looks like this:

public async createRows(table : string, columns: string | string[], values: string | string[]) : Promise<void> {
        let createPromise = new Promise<void> ((resolve, reject) => {
            this.db.query(`INSERT INTO ${table} ${columns} VALUES ${values};`, (err) => {
                if(err) throw err;
                console.log('Postgres: Rows were created...');
                resolve();
            });
        });
        await createPromise;        
    }

Edit 1:
There is error occurs (This function called from app.post, nickname, email and password has string values):

async function validationUsers (res : any, email : string = undefined, password : string = undefined, nickname : string = undefined) : Promise<boolean> {
    console.log('f:validationUsers email : ', email);
    console.log('f:validationUsers password : ', password);
    console.log('f:validationUsers : nickname', nickname);
    //validation: nickname and email
    if(nickname) {
        console.log('res.finished : ', res.finished);
        //let nickval : any = await db.readRows('users', 'nickname', `nickname = '${nickname}'`);
        await db.createRows('test', '(color, odor, taste, quantity)', '('meaningless', 'absent', 'sadness', 0)');
        console.log('res.finished : ', res.finished);
        /* if(nickval[0] !== undefined) {
            console.log('frofkofro');
            res.status(410).send('Nickname already exists');
            res.end();
            return false;
        } */
    }
    //validation: email
    if(email) {
        let emailval : any = await db.readRows('users', 'email', `email = '${email}'`);
        console.log('f:validationUsers if(email) emailval[0] : ', emailval[0]);
        if(emailval[0] !== undefined) {
            console.log("?00");
            res.send('Email already exists');
            res.end();
            return false;
        }
    }
    //validation: password
    if(password) {
        let passwordval = /^(?=.*d)(?=.*[a-z])(?=.*[A-Z]).{8,100}$/;
        if(!password.match(passwordval)) {
            console.log('password BAM!!!');
            res.status(412).send('Password does not match the criteria'); <-- **THIS STRING**
            console.log('password BOOM!!!');
            //res.end();
            return false;
        }
    }
    console.log('End of f:validationUsers');
    return true;
}

Edit 2:
Can it be some problem with pool.query or pool connection to database from "pg" library for PostgreSQL? Or maybe problem with ts-node compiler?

So, I really don’t understand what’s going on.
I don’t know if it’s important, but I use ts-node for compile and render typescript

Edit 3:
OKAY, so I started in new ts file new server with the same 5000 port and run THIS:

app1.get('/db', async (req : any, res : any) => {
  console.log('res.finished : ', res.finished);
  await db1.createRows('test', '(color, odor, taste, quantity)', '('meaningless', 'absent', 'sadness', 0)');
  console.log('res.finished : ', res.finished);
  res.status(200).send('All is fine this is send');
  res.end();
});

And result in console:

Connected to database as pool successfully...
Server started on port 5000
res.finished :  false
Postgres: Rows were created...
res.finished :  false

And POSTMAN received res.send(). wtf??????