(sidenote: I have no idea what hardware version my X60 setup is. It's not mentioned in the app, nor on the bottom of the device itself, so I selected V1)

Hello TP-Link community.

April 2024 I bought my Deco X60 setup. I started with 2 Deco X60's and a few months ago I 'upgraded' to 3 Deco X60's (full house coverage baby!)

My topology is as follows:

Backstory: Now for the first few months, I ran the 2 Deco's that I had (the bottom floor hallway Deco was not owned yet) in AP mode and let the ISP Router do basically everything. This worked really well, including no issues with the guest network, untill... November 2024, where the latest firmware (1.3.0) was causing a TON of IP address conflict issues. For no reason whatsoever, the "Smart-DHCP" within the AP's, that never gave any issue, could not deal with the DHCP server in the ISP router. This never happened before.

If I restarted the whole lot and then 1 by 1 starting it back up again ...
ISP Router -> Smart switch (which had no config, was left dumb) -> Deco living room -> Smart switch (which was also left dumb) -> Deco Office

... The whole setup would actually work again quite well for a few days. But shortly after, it would start to conflict again and leave most devices with 1 to 5 minutes without internet because it had an IP conflicted with another device on the same network.

So I contacted TP-Link support and they advised me to do a full reset of all Deco's and completely set up the network again. And whaddayaknow, it worked! ... for about a week.
Ironically, the ISP router álso had a firmware update, so to simply rule out which was causing the issue, I resorted in to buying another X60 and that resulted in the topology I posted above.

So I got to work, made sure the ISP Router put a DMZ to the first Deco X60 (putting the ISP router in bridge mode requires... a lot of contact with the ISP and patience...), the Deco setup was now in full Router mode and the Deco that was connected to the ISP Router became the "main" device/router 'that ruled them all'.

This actually fixed all my DHCP issues and other strange issues that I could not fully place. However, as I was reading through the documents, to make the guest network work you either had to:
A: Keep your Network Switches dumb.

B: Create a basic 802.1Q VLAN with number 591 and assign all the ports that need that VLAN to be ran through.

Option A was not working for my guest network. Connecting via the Guest network to Deco Hallway (main deco unit) and it worked absolutely fine. Connecting to any other Deco and the device would not get any IP address. The Main network Wifi and IoT wifi work flawlessly. And yes, the switches were dumb, really really dumb. (unmanaged)

So I tried a few things that people mentioned on these forums (It was specifically about the M5 Deco, but still, couldnt hurt) and I made the Deco's connect to eachother wirelessly and then check the Guest Network. And it works! Wait, why does it work now? I have no clue.

So, lets try Option B, (make 'em managed) because I need the switches (NAS device, Home Assistant and more are connected to one of the switches... And the network is simply faster and more reliable), I decided to Enable 802.1Q VLAN with VLAN number 591 on the switches and assigned to the required ports (basically the uplink ports + Deco satellite ports).

Let everything settle for a bit... Do a restart of all the switches + Deco's just in case... And... Nothing. Devices connecting on the Guest network through the satellite deco's still did not receive any IP address.

And that leaves us here. A bit in despair. I see multiple threads, from this year (August 2024 and newer) that have no resolution, nor any (useful, for my case) answers anymore from TP-link officials. So what is going on?! If anyone has a fix or a suggestion, please share. The guest network is not a massive priority, but I do like it when I invite friends over and they are not able to directly interact with my TV, NAS or other (semi-)important equipment.

Thank you for reading all the above.