Ring app notifies of a doorbell ring, but button not pressed

On several occasions, my phone has notified me of someone ringing the bell, but nobody actually is there. It’s definitely a false ring. What is strange is:

1, The phone uses a different ring tone to the one I set for a ring of the doorbell.
2, It shows a picture on the phone screen when the false ring happens.
3, The plug in Chime and Alexa Dot does NOT notify of this false doorbell ring.
3, When you open the App to see the timeline, the activity does not exist.

So it’s purely happening on the phone and uses the wrong tone - so I know it’s a false ring of the doorbell.

Any ideas to what causes this?