Ring Doorbell Pro 2 keeps freezing when on call

Ring Doorbell Pro 2 keeps freezing when on the call. Usually freezes after about 10-20 seconds and black screen appears. Can't connect back to view for about 1-2 minutes. Live View works fine but when I press "Green Phone" to talk to the person by the door, 10 seconds later screen goes black and Ring Bell freezes and I can't communicate with the person for about 1-2 minutes. Router is really close to the bell as it's behind the wall, so can't be any closer. In my old house router was much further away and all worked perfectly. Has anybody come across the same problem. Please help as really frustrating. Thank you