Checkboxes not checkable

Hi all,

I’ve a checkboxes field in a form made like this (only the extract):

  type: checkboxes
  name: dove
  label: Come sei venuto a sapere del corso?
      option1: false
      option2: false
      option3: false
      option4: false
      option5: false
      option6: false
      option1: Amici o colleghi
      option2: Internet
      option3: Social (faceboox, twitter,..)
      option4: Mailing list o forum
      option5: Volantini o pubblicità
      option6: Altro
      required: true

but both on localhost and in production the checkboxes are not checkable (a live demo here

The form plugin is updated and the grav version is 1.6.22.

Somebody has some hints?