Orbi Ethernet Backhaul causing broadcast storm

I too had this problem with V2.1.4.16 and ethernet backhaul.  I am running in AP mode behind a R7800 router.

The ethernet backhaul network must be dedicated to your ORBI devices.  If you have a switch between your main unit and satellites, no non-ORBI devices can be connected to that switch.  When ORBI devices see packets on the backhaul network segment that they didn't originate, those packets are forwarded to their other non-backhaul network interfaces.  If your switch is connected to both the backhaul and non-backhaul networks, you've created a switching loop and the network grinds to a halt.

In my house, I have a long ethernet cable run from where the ORBI router is to where the Satellite is located.  That cable is connected to ethernet switches on both ends where I connect other wired devices.  When I connected my ORBIs to each switch with a single cable, I created two backhaul networks: one provided by the ORBIs and the other provided by the switches.

To fix, I just connected the ORBIs between the switches instead of "outside" them like so:

Router -> Switch -> master ORBI WAN port -> master ORBI LAN port -> Long dedicated ethernet run -> Satellite LAN port -> another Satellite LAN port -> Switch -> other ethernet devices

The important thing is that each ORBI unit has two ethernet cables connected.  One for the backhaul network and the other for non-backhaul traffic.

My bandwidth tests with iperf3 show no performance hit between my two switches with the ORBIs in the middle.  Wireshark confirmed a happy network.

I think the Netgear wiring diagram cited by the OP did not expect anything else to be connected to the switch between the main ORBI unit and the satellites.

I hope this helps...