Hello @tiziano,
It seems that you can no longer deactivate a form by returning self.deactivate() in the validate function anymore, even though the Rasa doc says you can:
You can also deactivate the form directly during this validation step (in case the slot is filled with something that you are certain can’t be handled) by returning self.deactivate()
Check this accepted answer to see if it can solve your problem: Restart conversation inside validation function
@Tanja What do you think about editing the Rasa document about this ?