(Hence you haven't discovered a rogue DHCP server yet.)
I'm not confused...and you still haven't answered the question(s) that could easily clear DHCP server/lease discrepancies. I suppose you dont see how the questions are relevant; or this is a kind of troll?
Are these devices set up to default to .253?
That it what I would have also thought in the first place.
I actually checked my device side in depth already but at is has a "read only" flash it can't even keep it's DHCP information cached when turned off hard (this it what probably happen, at least my wifi went down while most lights survived the outage which was roughly a second).
So my assumption was therefor that my WDS repeater was "faster" available then my main router which does dhcp.
Thank's for the tip but that will not be possible on a short run. Power outages (even if they are only very short) are quite common in my area. I rather want to make my system resilient so that it can handle such ungraceful situations.
My old setup with WDS repeater + router with stock firmware didn't had such problems so I'm quite confident this can be solved in software/configuration.
Could be the WDS repeater configured that they just spawn an AP when the uplink connection is established (because then the upstream DHCP server will be available too)?
That's the DHCP server on the router. So .111 to .254 should be served?
When the main router is down (and with it, the DHCP server), what is one of your clients showing for the following:
(you may need to force this situation -- take your main router offline for this test and then force one of the hosts to renew its DHCP lease)
Does this also means you refuse to find the rogue DHCP server, or explain what software is recording these IPs?
I'mma stop responding til you answer the simple questions that would resolve the problem immediately:
(If you identify this, you no longer have to guess or play about where the lease is coming from. You not answering these questions lead me to think you're not serious.)
Why does your WDS repeater have a DHCP server enabled!?!? 
This is the problem!
Disable this - problem solved.
It does not have a DHCP server enabled like already stated in this thread 
How do you come up making such a false assumption?
That would be very nice of you. Your posts here always contain this destructive notes and I'm not entirely sure what your intentions really are. All other people in the thread can help and advise without being passive (or active) aggressive.
Thank's, that sounds like a plan. I will do this, probably even make a little test setup for it so I can get logs from my client and logs from openwrt. Maybe something interesting is there to find 
Well, since you edited the exact sentence, and it still implies that there's a DHCP server:
No matter how you word it, it would help if you explained htis.
Why won't you just tell us:
"when I connect a device, it gets an address, and the DHCP server has x IP and y MAC"
???
I would be really grateful if you would stick to your words and
in this thread. Thank you for all the effort and thoughts you provided.
I have some news as the same problem occurred again and this time I could identify the roaming of the client and the IP's it was served:
Turns that the ap (lila bssid) which is powered by poe actually can overcome short power outages while the main router (brown bssid) will turn off right away and with it it's DHCP server.
Still I have no idea why the ap (which doesn't have any dhcpv4/6 server enabled) is even able giving away DHCP leases(
) as with my configuration intended it should only "delegate" this work to the configured gateway (the main router) 
Some configs of that ap (21.02.2) which only has one lan interface:
you were recording using Homeassistant?
Rather Home Assistant were recording for me 
Using this? I wish more data could be pulled/pushed into HA from OpenWrt.
I tried to play my part, but it seems devs are not interested.
@MangoMan aam aadami how can I PM you?
It's a bummer indeed that my former (commercial, non foss) router had superior ha support and it was a ease to locally get data in real time from it.
I didn't even waisted a second thinking that openwrt would be a "downgrade" in that regard - but it sadly was. Weird that some commercial router firmware works better with a foss software than the foss router firmware does.
I suppose the issue is really that not enough people want this tool. If they did it would receive more attention. Those that make contributions are just enthusiasts doing stuff for fun and mostly without payment. And also there is a big case of fixing stuff that affects oneself. I have spent ages on the CAKE autorate stuff because I want that to work really well for my own connection.
I haven't come across commercial offerings that beat what I can set up with OpenWrt and even if I could find one I'd totally miss the amazing expert community we have here. I mean look at guys like @trendy and others. You can ask really convoluted and obscure questions and get detailed and helpful answers. Then there's the flexibility that comes with open source. Things can be changed in a dynamic way that is not so easy with rigid processes associated with commercial offerings. One can also learn a lot with OpenWrt.
I think the collective brain power of this community is immense.
This is the beauty and crux of open-source software, you can contribute with your idea and software codes, but at the same time, you are bounded by what is available, which depends on the developer's time and experience, e.g Netgear and Asus have better support/ features in Homeassistant while OpenWrt is only used for tracking devices/presence sensor.
On the topic of forum support, there are quite a few members, without whom OpenWrt couldn't be noob friendly to name a few @frollic @pavelgl @slh and @trendy. 
but then there are some members in other forums e.g in DD-WRT, whose signature line for each noob's Question is "Google that" 
That was one reason why I didn't go with DD-wrt, even though a guide already existed for it for my purpose.
I wrote the OpenWrt guide itself with the help of the forum's members
You can verify if a dhcp server is running or not: netstat -lnp | grep 67
With a packet capture, like tcpdump or wireshark, you can see which one is the server offering the lease.
was it Unifi ?, only that seems to have this level of features in Homeassistant
(For some reason, the OP won't simply do this; nor any thing else that could easily identify the specific device...and won't explain why.)
e.g. A Windows PC/laptop clearly displays the identity of the DHCP server that issued the IP when running commands/buttons to show the network information
Edit: also the OP claims I gave some word. That is clearly untrue; and in good conscience, I wouldn't stand by while others' valuable time is wasted repeating the same troubleshooting suggestions they refuse to attempt. Others can choose to continue assisting, the same as before this post.
