@TP-Link 

I am not @GrumpyOldGeek, but i have the same problem and debugged me the ass of, simply not awaiting that kind of mess.

As i bought 3 deco m5, i had a double nat network (internet <-> isp cable modem/router <-> master-deco in router mode as dhcp server <-> switch, local network, powerline distribution as backhaul for the other two decos.

It worked fine, but than i needed full ipv6 for some projects, and thats not (easy) possible with double nat. 

So i deployed a system with ipv4 dhcp and dns, which announced the isp router as gateway and switched the decos to ap mode, and the problems started.

First it looked for me like a looping thingie/broadcast storm in the network, my switches flashed on all ports parallel in that moments, i suspected problems with looping by wifi and backhaul (which was never a problem in router mode), but after some sleepless nights of investigation i found devices with totally different ip addresses and wrong dns and gateway announcements. 

I derusted my tcpdump skills and setup some raspi probes in my network to track bootp/dhcp and related packets and i found, that the decos acting sometimes as dhcp servers. WHAT THE F*CK? 

I googled me to this thread, and it looks like my problem.

I make heavy use ip over powerline to reach all sections, and it is sometimes somewhat unstable (it does not matter at typical usage as surfing, streaming, but there are possible short dropouts and i note them in my monitoring) as i have to bridge longer distances).

So you dont need to know my or the other affected guys manufacturer of their isp modem or something, just take in account that network is not 100% reliable and most components are aware of that without your smart nonsense.

Please note that your smart dhcp is not smart at all but against all dhcp/bootp related ietf standards and you broke the standards in full knowledge.

I am very happy to find that thread, but i am also concerned that you promised a fix 10 month ago and nothing happend so far.

I am not convinced that you will fix this in a forseeable future, and i will try to get rid of these units as fast as possible.

They are great and affordable for the default router usecase, but cheap for the wifi-ap usecase (which is in fact the more easy one, but you decided to f*ckit up).