Transaction entity manager does not commit some data

Question

I've experienced an issue regarding TypeORM transactional entity manager. Below is the code snippet.

class Fizz extends BaseEntity { 
  ...
  buzzId: number;
}

class Buzz extends BaseEntity { ... }

class FizzService {
  createFizz(input) {
    return Fizz.create(...input);
  }
}

class BuzzService {
  createBuzz(input) {
    return Buzz.create(...input);
  }
}

class FizzResolver {
  async generate(payload) {
    await dataSource.transaction(
      async (transactionalEntityManager) => {
        let fizz = fizzService.createFizz(payload.fizzInput);

        const buzz = buzzService.createBuzz(payload.buzzInput);
        await transactionalEntityManager.save(buzz); // sometimes persists the data, but sometimes not
        
        fizz = Object.assign(fizz, { buzzId: buzz.id });

        await transactionalEntityManager.save(fizz);
      }
    );
  }
}

Given this code, I was expecting that if there were any error a rollback would happen which would not commit anything. Anyway, what happens is sometimes the Buzz entity record is not persisted but I still have the generated id in the Fizz entity record.

Any idea on why?