Might not be either in your case, but this has happened to me a couple of times. The first time, it appeared that my phone network switching from 'poor' wifi to data at just the wrong time was causing the issue (despite it appearing that the camera couldn't register with Ring) - disabling it worked. The second time, I never did work out what the issue was - I just kept trying. Eventually the device registered/was connected, even though it said it had failed!