Ansible bug with datetime in data

data.yml

---

data_1:
  - id: 1
    key: hello
  - id: 2
    key: world

data_2:
  - id: 1
    key: 2020-10-18
  - id: 2
    key: 2020-10-19

...

playbook.yaml

- hosts: localhost
  become: no
  vars_files: data.yml
  tasks:
     - debug:
        var: item.id
       loop: "{{ data_1 }}"

     - debug:
        var: foo.id
       loop: "{{ data_2 }}"
       loop_control:
         loop_var: foo