Access denied for user 'root'@'localhost' with two DataSources in context.xml

I'm facing a problem with Java 8, MySQL Server 5.7.23, MySQL Connector for Java v5.1.45 and Tomcat v9.0.12 (running on Ubuntu Server 18.04).

I've built a simple Java application (war) that executes a query in a MySQL database.

My context.xml (I've put 2 resources nodes, one for production and one for developing environment), from the real application scenario I read from CATALINA_OPTS a parameter called "env" and reading it with System.getProperty("env"), the application can choose the appropriate datasource to use.

<Context>
    <!-- MySQL - Production -->
    <Resource
        name="prod-jdbc/ds-1" auth="Container"
        type="javax.sql.DataSource" factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
        driverClassName="com.mysql.jdbc.Driver"
        url="jdbc:mysql://localhost:3306/testdb?useSSL=false"
        username="dbuser" password="dbUserPwd!"
        autoReconnect="true" maxTotal="10"
        minIdle="3" maxIdle="5" maxActive="10" maxWaitMillis="10000"
        removeAbandonedOnBorrow="true" removeAbandonedOnMaintenance="true"
        logAbandoned="true" removeAbandonedTimeout="1000"
        closeMethod="close" testOnBorrow="true"
        testWhileIdle="true" timeBetweenEvictionRunsMillis="60000"
        validationQueryTimeout="10" validationInterval="6000"
        validationQuery="SELECT 1"
    />

    <!-- MySQL - Development -->
    <Resource
        name="dev-jdbc/ds-1" auth="Container"
        type="javax.sql.DataSource" factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
        driverClassName="com.mysql.jdbc.Driver"
        url="jdbc:mysql://localhost:3306/localdb?useSSL=false"
        username="root" password="root"
        autoReconnect="true" maxTotal="10"
        minIdle="3" maxIdle="5" maxActive="10"
        maxWaitMillis="10000" removeAbandonedOnBorrow="true"
        removeAbandonedOnMaintenance="true" logAbandoned="true"
        removeAbandonedTimeout="1000" closeMethod="close"
        testOnBorrow="true" testWhileIdle="true"
        timeBetweenEvictionRunsMillis="60000" validationQueryTimeout="10"
        validationInterval="6000" validationQuery="SELECT 1"
    />
</Context>

A simple tester class:

package main;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.sql.DataSource;
import javax.ws.rs.core.Application;

public class ConnectionTester extends Application implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent arg0) {
        Context ctx = null; Connection con = null; Statement stmt = null; ResultSet rs = null;
        try{
            ctx = new InitialContext();
            DataSource ds = (DataSource) ctx.lookup("java:/comp/env/prod-jdbc/ds-1");
            con = ds.getConnection();
            stmt = con.createStatement();
            rs = stmt.executeQuery("SELECT nome FROM Customers");
            while(rs.next()) {
                System.out.println(rs.getString("name"));
            }
        }
        catch(NamingException | SQLException e){
            e.printStackTrace();
        } 
        finally{
            try {
                rs.close(); stmt.close(); con.close(); ctx.close();
            } catch (SQLException e) {
                System.out.println("Exception in closing DB resources");
            } catch (NamingException e) {
                System.out.println("Exception in closing Context");
            }
        }
    } // contextInitialized
} // ConnectionTester

I've set MySQL permission this way (I also need to allow external access for "dbuser" because I have an external client that connects to this MySQL database):

ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'veryStrongPwd';
CREATE USER 'dbuser'@'localhost' IDENTIFIED BY 'dbUserPwd!';
GRANT ALL PRIVILEGES ON *.* TO 'dbuser'@'localhost' WITH GRANT OPTION;
GRANT ALL PRIVILEGES ON *.* TO 'dbuser'@'%' IDENTIFIED BY 'dbUserPwd!' WITH GRANT OPTION;
FLUSH PRIVILEGES;

Tomcat doesn't have any specific configuration or resource configured, it's simply the v9.0.12 unzipped in a folder.

I've tried to put in context.xml both the "root" and the "dbuser" credentials but when I start Tomcat, I get the following problem:

ConnectionPool.init Unable to create initial connections of pool.
 java.sql.SQLException: Access denied for user 'root'@'localhost' (using password: YES)
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:965)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3973)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3909)
        at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:873)
        at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1710)
        at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1226)
...

And after throwing those exeptions, it prints the recordset, but why does it require the root login even if in the context.xml I set dbuser credentials?

I've read searched here in StackOverflow and I've read that I've to check the mysql.user table, if I run:

SELECT user, host, plugin, authentication_string FROM mysql.user;

I get this ("plugin" column has "mysql_native_password" value for every record):

If I try to login into MySQL server from the shell with:

mysql -u root (or dbuser) -p

I can login succesfully.

EDIT: I've found that deleting the second "Resource" node from context.xml (the one made for development environment), the problem disappears, but I still don't uderstand why it happens because in the lookup I choose the prod resource (ctx.lookup("java:/comp/env/prod-jdbc/ds-1")).

What am I missing? Thanks in advance