Terrible Bug - Adding a RBS20 satellite to RBK 50 system breaks the LAN

Following up from another thread- I just got done with a full troubleshoot and it appears that Interoperability between Orbi systems is rather badly broken.

Many users may not even notice this as this issue affects only LAN-LAN communication between mesh nodes while WAN-LAN works unaffected across the entire network

Background - 

I had a RBK50 (RBR50 and RBS50 ) that had been running fine for 2 years with a couple of firmware upgrades and minor woes in between. 

I had some blind spots in my porch so I decided to add another satellite - Since the RBS50 is expensive where I live and I was getting a great deal on amazon, I brought a RBS20 as I didn't need anything more than 200-300 mbps in the porch anyway.

Netgear claims Interoperability between different Orbi systems so I assumed the RBS20 is a no-brainer for my use case.

Bad call!

Adding the RBS20 was rather easy and I was able to add the satellite within 10 minutes - everything seemed absolutely fine to begin with. Internet was fast everywhere but by evening, I realized that a bunch of my LIFX and Hue lights were not responding .

Initial tests showed even more odd behavior e.g. Inability to ping various devices even though WAN access was fine across the board

Testing and Results

4+ hours of troubleshooting and i realized the problem runs deeper - All devices that were connecting to the RBR50 could connect to the Internet fine, However devices connected to the RBR50 could not reach other LAN devices and vice-versa.

All devices are on 192.168.5.0/24 subnet and there are no IP conflicts. All Orbi devices were tested with bost test cases of DHCP and static IPs assigned addresses

I swapped all switches , pulled out a bunch of old switches to see if the issue was with something else but no-go.

I rolled back the firmware on all Orbis, reupdated to latest, performed a full reset but no-go

8+ wasted hours later, I unplugged the RBR20, removed the satellite from the RBR50 and rebooted - Voila! Everything was back to normal!

I have attached a rough network diagram if it helps understand the topology - it's a moderately complex setup but nothing too crazy.

Apologies for my pathetic drawing skills - 30 years ago, my drawing classes at school used to be my worst nightmare :)

Edit: There is a (probably irrelevant) typo in the drawing - The wireless backhaul labels are swapped incorrectly