Ansible - become: true - not becoming root on server

I am not sure if this is the right stackexchange site. Please let m know, if I should ask it on other forum and which one?

I need root access to perform an action, so I tried to use become: true

- name: Modify server.properties
  hosts: kafka_broker
  become: true

  vars:
    ansible_ssh_extra_args: "-o StrictHostKeyChecking=no"
    ansible_host_key_checking: false

  tasks:

    - name: I am confused
      command: 'whoami'
      register: myidentity

    - name: my secret identity
      debug:
        msg: "{{ myidentity.stdout }}"

    - name: "Add the line if it does not exist"
      become: true
      tags: addifnotexists
      lineinfile:
        path: /etc/kafka/server.properties
        line: "ssl.enabled.protocols = TLSv1.2"
        insertafter: EOF
        state: present
        backup: yes
      register: addifnotexists
    - debug: var=addifnotexists

One one set of servers, the user is actually root, on other set it is the account from which the script was executed.

    TASK [my secret identity] *********************************************************************************************************************************************
    ok: [server016] => {
        "msg": "svcacct"
    }
    ok: [server031] => {
        "msg": "svcacct"
    }
    ok: [server033] => {
        "msg": "svcacct"
    }

Other set of servers

    TASK [my secret identity] *********************************************************************************************************************************************
    ok: [server010] => {
        "msg": "root"
    }
    ok: [server011] => {
        "msg": "root"
    }
    ok: [server012] => {
        "msg": "root"
    }

Is this difference in the output due to any difference on the server set-up? What do I need to ask the systems admins to check or set-up

Thank you for any pointers you can provide