Error creating database pool not creating session

Question

Development environment: nodejs
Library: oracle-db 
Oracle Version : 9i

The test and error occurrence codes are as follows:

const oracledb = require("oracledb");

async function hello() {
    await oracledb.createPool({
        user: "test",
        password: "1234", // myhrpw contains the hr schema password
        connectString: "127.0.0.1/ORCL",
        poolAlias: "ora1",
        poolIncrement: 0,
        poolMax: 4,
        poolMin: 4,
        poolPingInterval: 30,
    });

    const connection = await oracledb.getConnection("ora1");

    const result = await connection.execute(`SELECT IDX FROM MYTABLE WHERE number= '000000000'`);

    console.log(result.rows);
    connection.release();
}


hello();

The database pool was created with this code. And after the test, four sessions were created and confirmed to work well. However, an error occurred due to repeated execution of the code. If only three or fewer sessions are created when creating the pool, the following error occurs:

(node:27732) UnhandledPromiseRejectionWarning: Error: ORA-12170: TNS:Connect timeout occurred
(node:27732) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:27732) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

In order to check what kind of error has occurred, I have tailed the file below.

#tail -f /oracle/app/oracle/admin/orcl/bdump/alert_orcl.log
#tail -f /oracle/app/oracle/product/9i/rdbms/log/alert_orcl.log

However, no logs were stacked and no errors were seen. Could you possibly help me?