This has been (and still is) being investigated by support and engineering. Currently running beta firmware 9.12.4.1101_1.3.17 which hasn't helped at all.

I'm not able to test with the system in Router mode as that would involved huge complications and disruption to my network. And anyway, router mode is of no use to me - I need AP mode.

The NetGear system is not connected to the ONT. My wired router (NetGate 6100) is connected to the ONT and the Orbi router unit is connected, via switches, to the router.

I have CAT-6A everywhere and the Orbi is using 10 GbE wired backhaul via a 10 GbE NetGear switch.

All iPhones and iPads are using native MAC addresses (private MAC addresses are disabled) as I assign 'fixed' IPs to all devices using DHCP static reservations.

Devices range from iPhone 12 through to iPhone 16 Pro and from iPad gen 7 through iPad Pro 13" M4 plus a bunch of watches (series 6 through 9).

Upstairs is approx 61 m2 (650 sq ft). Downstairs is approx 81 m2 (872 sq ft).

Distance between units is ~10m (33 ft) horizontal and ~4m (12 ft) vertical, though as I;m using wired backhaul that should be less of an issue.

I think part of the problem is that they didn't;t really put much thought.effort into AP mode; lots of limitations and bugs. AT this point (6 months in and still flaky as hell) I think I'd be better off with a product designed from the ground up to be an access point (or mesh of APs) rather than one where it is clearly a second thought. Even if they can solve the stability issues and IPv6 connectivity problems I'm still left without usable guest network capability.

An interesting data point is that prior to deploying the Orbi system my WiFi was provided by 3x Apple AirPort Extreme 802.11ac units (all running in AP mode) which provided both main and guest networks. Apart from a few places in the house where signal was a little low, and overall speeds being a bit middling, that was a rock solid setup with zero issues.

Feature request - LB2120 LTE Router -use mobile broadband by default and failover to wireline