Wow way to blow smoke! I have this problem too, with the same router and doorbell device that have been functional for years. Only the doorbell has this issue other camera are fine. This issue is not solved, to mark it as such is a slap in the face of paying customers. If you do not interrupt the process with a failing live view it works correctly, but if you try to look at the event before it has uploaded to the cloud server, it becomes all black. This is a bug on your end, you need to admit it. Get it fixed or refund some of my money I paid for cloud service.
Sincerely,
Angry Customer.