Ring pro power and offline issues (UK)

Just fitted a ring pro doorbell to my house. There was no doorbell previously fitted so I have taken the power supply from a 240v socket, up to a switched fuse spur (just so I can isolate the power to it if needed) then to the supplied transformer and on to the bell. At first it lights up and connects to the Internet for a few minutes, but then it goes offline and the bell won't light up or do anything. We took it off the wall last night and plugged it in to the USB port on the side and it stayed powered on and connected to the Internet all night. What could the issue be? Cheers for any help.