Siri speaking at all hours

Since my son updated his iPad, siri has started calling out at random times (usually midnight or 1am) usually saying ‘I am trying to wake you up’, or once even ‘what is the point of all of this?’.

There are no alarms set on his iPad and I have turned off the toggle that allows Siri to be summoned when the iPad is locked. Any ideas of how we can stop this creepy Siri voice in the night??