I'm new to RBE970/971 but old to all this netz stuff

Sorry.. in rushing I failed to see your other questions:

• The house over these past 20 years has every Cat # from 5, 5e, 6, and 6a. I run the Orbi backhaul over Cat 6A.  STP is unnecessary, speaking as an "EE". Shielding is only useful if it is properly grounded. "Proper Grounding" however, is a simplex transmission problem! You ground shields at the differential input circuit, not the output circuit.  This is classic in the design of RF and instrumentation equipment. The goal is to short the non-common mode noise over the cable at the point just before the input. Common mode noise is dealt with by the twists in the pairs. The dif amp at the input cancels that noise out. If you look up special twisted pair cables you would see a shield over each directional pair so you ground at the appropriate end. Category cable was never this precise so you see just one shield over all conductors. The theory would have it, that if you wish to ground that cable as well as you could possibly do, it would be grounded in the absolute center of its length! HA HA. Reason being tis that you would only have non-common mode noise picked up over only HALF of the cables run. 
• Long convergence time to recognize nodes on the Orbi control plane goes well beyond wiring. All cables were validated (that's well beyond pin continuity checking) at 1 Gbps using 1 minute BERT testing. Just an FYI... you can run 10G on 30 feet of Cat 5e! it's about two things: (1) "puffs per foot" that is pico farads per foot and (2) whether the terminations at each end were done properly to avoid Near and Far End crosstalk. I've had the fortune/misfortune to design/review/test cables for huge IBM, AT&T and BlackBerry data centers (hundreds of thousands of cables). 
• Don't have floor plans but what most folks will dwell on are distances when the more important factor is construction composition. I've had a job where standing on each side of a single wall had ZERO WiFi signal when there was only 4 feet between router and access point. Problem was it was prior home owner was an engineer and built a Faraday cage - 6-in thick concrete wall with embedded wire mesh. But my problem is not about devices. It's about the router not seeing the satellites over WIRED backhaul, albeit 6 satellites. 
• Distance (independent of construction composition) AND if on the same floor would be around 30 feet. My radio goal is to have an RF signal around -40 to -50 dbm signal in the places where the home owner works, sleeps, sits. This is what I achieved with the system I installed. 
• You're right:  Disabling dynamic MAC is correct per Apple's recommendations - but this will not help the situation of the satellites connecting to and disconnecting from the main router. 
• I'm happy that you are able to get excellent wifi in your home. I started in commercial telecom in 1975 (telex & telegram). Worked my way to be responsible for IBM Global Network, later AT&T Global Managed services and then BlackBerry's infrastructure engineering. Today, I do smart home/networking in residential for the past 20 years. I retired my corporate engineering position 10 years ago where building data centers and transmission systems and dealing with Cisco, Avaya, Juniper, Lucent Technology and every carrier in 60 countries was my executive responsibility.
• Your points are very valid.

I do think however, this problem is an inner control plane problem coupled with a limited design for mesh implementation. The interior problem is what causes the known state of the RBS and RBR to not 'know' if they are up or down and what the best path to get between two points on their interior graph is. That coupled with a questionable implementation of mesh and the roaming that needs to happen. Adding 'management' to these is also a likely sore point in this design. They were in a max of 4 satellites since the introduction of ORBI while their competitors have already achieved as many as eight (ASUS). {By the way, it took ASUS over 3 years to figure it out, so this is not a trivial problem. "Mesh routing" was only introduced in mid 2010's for the commercial accounts. and much later for residential use.} 

@Furye38: thank you for your insightful posts. Yours, donawalt and OrbiTechDude's allowed me to figure out what I had to do... much appreciated. ... marcel