Orbi RBR750 doing odd DHCP things

Thanks to all of you for your input and advice.

So many supplementary questions: I'll try to address them all if I can.

I established that the Orbi router was to blame through brute force. The error only happens if the Orbi is connected, never when it isn't. There's nothing else on the network capable of functioning as a DHCP server, apart from the Genexis.

Can I describe the topology? Well, one cable runs straight to the front hall from the Genexis router. No switches, no patches, simply one long cable.

Another runs to a switch in the small garage, this gives off a “spur” (if you will) to more switches and kit in the big garage and connects to the cable which runs to the attic where there is ... another switch.

I have tried a number of different schemes: Orbi Router in the hall, satellites in the attic connected to the switch there; RBR in the attic, connected to the switch, one satellite in the attic wired straight to the RBR, the other in the hall; the attic feed from the garage going to the RBR and running everything distal to that point from connexions to the RBR...

What *used* to work was having a satellite in the hall (connected directly to the Genexis router) apparently invisible to the RBR, but nonetheless working as a good access point, with the RBR in the attic, connected to the switch there by one cable and the other satellite (which the RBR could see) also connected to the switch.

Right now (fingers crossed, it's been up for eight hours and still works) the RBR is in the hall (direct connexion to the Genexis) and the satellites are up in the attic, each connected to the switch. All three APs work and have the same wireless SSIDs on the same channels.

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The Genexis router provides the following information:

Platform Lunar

Product name DRG7820

Product number 99615010

Product date December 19, 2017

Hardware revision 1.2

Serial number W.0617493842

Bootloader revision bootloader-lunar-3.2.0-R

Firmware revision geneos-lunar-3.17.0-R

It's not broken. I'm not going to try to fix it. It's always stuck to its configuration as 192.168.1.1

Before installing the latest firmware I was on V3.2.18.1_1.4.14. If I remember correctly - this was three years ago - I tried V4.6.3.16 and it caused me more problems so I forced an installation of the older software.

The whole setting up nightmare took an entire weekend, so once it was working I left well alone.

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Somebody asked - I don't see their post now, for some reason - how I knew that something was handing out 192.16.10.xxx addresses. It was nothing sophisticated, when my Android 'phone says “connected without internet” there's a little cogwheel icon, press on it and there's the option to log into the router which was set to 192.168.10.1 - There is nothing in my network at that address.

Getting system details for the 'phone showed that it had been given addresses like 192.168.10.19 - hence “connected without internet”.

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Someone wanted to know (again, I don't see their post now, as I look at the forum) if I was on a class B or C network. I have to confess that I set the network mask to 255.255.0.0 today (/16) but only to try to aid trouble-shooting. Pinging 192.168.10.xxx from a 192.168.1.xxx/24 network wasn't going to be very helpful, I didn't think. The ridiculous mask (for such a small system) came after the errors.

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I should emphasize that I know precious little about networks. I tend to do a bit of reading when I have a problem and otherwise get on with things that I'm more competent to deal with. I'm pretty sure that a network guru would not be happy with the way that my little network has evolved. But, it did work for three years, until it didn't.

Is there any alternative software for the RBR750, other than Netgear's own?

[It seems that my post has been automatically changed to remove invalid HTML, but I cannot see what's missing]