Netduma Fraser

Are you using PPPoE/VLAN or IPv6 at all?

We don't really have any recommendations for third party equipment but any should work well

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On the loading screen does it give you options such as reboot, continue anyway, get logs etc? If you unplug the router from power for 10 seconds, plug in, wait 4 minutes then access can you get in then? What firmware version are you on currently?

Yes you're on the latest firmware currently. Steady Ping is a DumaOS 4 feature and DumaOS 4 won't be coming to the XR range unfortunately.

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You said you had the R1 in the DMZ on the ISP router - this is the WAN IP from the System Information page? And you mentioned you had port forwarding rules as well, is that still the case? If so remove those and check again

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Yes on the router

There aren't any specific settings other than the ones that have been mentioned that would block it, try disable Adblocker though and see if that helps

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Always On or Auto in most cases

You don't need to use three routers, just the Linksys or the XR1000 to handle PPPoE, then put the R3 WAN IP in the DMZ of that device, reserve the WAN IP of the R3 on that device. Reboot the main router, wait 2 minutes, reboot the R3, wait 4 minutes then check again.

I doubt it, having the router specifically determine the connection method behind APs is difficult as is as they appear to be connected via ethernet. They will still work even showing offline as far as I am aware

I'd suggest following this guide https://support.netduma.com/en/support/solutions/articles/16000074717-how-to-test-your-internet-ping while downloading/streaming etc and start with a high value for Congestion Control (set to Always), say 95% then check, decrease by 10%, check, decrease by 10% etc, until you get to a value that is pretty good and then try 5% either side of that value to see if it can be improved. It's important to note that Download & Upload on Congestion Control don't have to be the same value and that you may have a better experience with differing values. This will be a more real world test.

Factory reset then don't change any settings, does it work then?

Disable QoS fully, does it continue to happen then?

Yes that's what I believe is the case, when connected to an AP, for all intents and purposes the R3 sees the device as connected to the R3 itself. As the R3 doesn't have 6GHz and thus has no way to recognize that kind of connection it doesn't display it, though of course technically the Eero gets the internet and passes it on to the laptop so it will have internet through the R3 it will just appear as an offline device.

What do you mean by the Geo-Filter method? Does it work with the Geo-Filter disabled?

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If you disable the Geo-Filter do you get the same error?

It'll just be a case of fine tuning the percentage for upload - as your upload speed is a lot lower it is easier to saturate and for bufferbloat to occur so you may need to be more or less agressive with the percentage for it

Do a video of what you're seeing that would explain what's happening

Have your ISP modem/router or another router handle PPPoE instead of the R3 then remove PPPoE from R3/switch it to DHCP then that will raise your speeds through the R3