Message placeholders not working using winston container

Question

I'm trying to use winston container but the message formatting doesnt seem to happen.

Using the 'createLogger' approach i can see it works

const consoleTransport = new winston.transports.Console();

// logger object with above defined options
const logger = winston.createLogger({
  transports: [consoleTransport],
  format: winston.format.combine(
    winston.format.splat(),
    winston.format.simple(),
  )
});

logger.stream = {
  write(message) {
    logger.info(message);
  },
};

logger.info("This is my placeholder %s", "test");

I can see the output is correct

info: This is my placeholder test

But using a container

const consoleTransport = new winston.transports.Console();

// Create a container and set the format at the container level
const container = new winston.Container({
  transports: [consoleTransport],
  format: winston.format.combine(
    winston.format.timestamp(),
    winston.format.splat()
  ),
});

// Create a logger within the container
container.add('test1', {
  level: 'info',
});

const log1 = container.get('test1');

log1.info("This is my placeholder %s", "test");

module.exports = container;

The formatting doesnt work... what am i doing wrong?

{"level":"info","message":"This is my placeholder %s"}