Wired Backhaul Intermittent after Reboot

WAP - You clearly already know this, but I'll just be explicit. You can't use the wired backhaul system reliably. It's a poorly implemented feature and there's nothing you can do about it.

You've provided greate detail in your steps, and you've done everything as a rational person would. However, it's not going to work. It was a feature they rushed out without bothering to check if it would work properly. Basically, the theme of the Orbi's.

I have a RBK53 system and tried a wired setup. I had similiar expeirences. I gave up. Went with the a Unifi system. No problems since.