Docker port exposure with IP resulted to slow postgres database connection

Question

I set up a Docker compose file with two Postgres database services, one for production and one for testing. When exposing the ports from container to host I started with following compose file

networks:
  db:

volumes:
  db_data:
  db_data_test:

services:
  postgres:
    image: postgres:16
    hostname: postgres-hostname
    networks:
      - db
    ports:
      - 127.0.0.1:5432:5432
    volumes:
      - db_data:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready", "-d", "db_prod"]
      interval: 30s
      timeout: 60s
      retries: 5
      start_period: 80s
    env_file:
      - ../.env
      
  postgres_test:
    image: postgres:16
    hostname: postgres-hostname
    networks:
      - db
    ports:
      - 127.0.0.1:5433:5432
    volumes:
      - db_data_test:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready", "-d", "db_prod"]
      interval: 30s
      timeout: 60s
      retries: 5
      start_period: 80s
    env_file:
      - ../.env

Using when running my application with these databases, I experience very slow (~18s) execution of the database migration method I use to initially create my database before each unit test using the database.

When I removed the 127.0.0.1 the execution time dropped sharp to what I expect (<1s).

I'm not very familiar with the inner workings of Docker or ports on my host. Would be great if someone can explain what happens if I put 127.0.0.1 before the host port.