@Winterland 

Hi, welcome to the community.

I think the current issue is also related to the private address/randomized MAC addresses and the "unknown" device is actually a home device in disguise.

Alexandre has a very precise explanation here about this feature, which might help to understand what happened in your case:

https://community.tp-link.com/en/home/forum/topic/576100?replyId=1119002

 He is right that there hasn't been a better solution for this case unless users are willing to disable the randomized MAC addresses feature on each device.

And The "Whitelist" feature request currently has not been accepted yet.

The most promising feature that I have received and is also under consideration now, is a pre-set parental control profile for new devices and users could customize the permission per their needs.

It is also highly appreciated if you have any other better ideas.

Thank you very much.

Best regards.