first element triggers a message, second element does not

By the way, enabling or disabling Ajax makes no difference...

Please provide the YAML of a small form that exhibits the bug but without extra form fields.

Ok, I leave only two steps and as less code as possible, sorry if there are still unnecessary things...

Thanks!

I am confused by using the 'unchecked' trigger for the 'addlabel_02' textfield.

    addlabel_02:
      '#type': textfield
      '#title': 'Your label'
    incorrect_label_02:
      '#type': message
      '#states':
        visible:
          ':input[name="addlabel_02"]':
            '!value': 'H*'
        invisible:
          ':input[name="addlabel_02"]':
            unchecked: true
      '#message_type': error
      '#message_message': '<strong>Wrong!</strong><br>until correctly labelled'

Sorry for taking so long to answer, (doing some other stuff)...
So the condition "unchecked: true" → while no character is introduced the message is hidden
I could not add it the other way around because "visible" was at the previous condition...
I hope I explained clear enough!!