I'm having the same problem.

Recently I updates the firmware on my Decos, and I've noticed that the DHCP Server stops running on my network. When this happens, devices start getting bogus 169.254.x.x IP addresses. I ran tcpdump -i en0 -n port 67 or port 68 on my network and triggered some DHCP lease renewals from my machine to see if anything responds, but nothing does. This indicates that there is no DHCP Server running on my network, despite it being set up in my Deco app.

I have my network set up with the main Deco at 10.0.0.1 and configured to issue DHCP IPs in the range of 10.0.0.100 - 10.0.0.250, and if I reboot my entire network, devices are able to get assigned IPs in that range for a short while. Eventually, it seems like the DHCP Server crashes, because at some point nothing is able to get dynamically-assigned IPs.

I really hope someone from TP-Link sees this because my network has been totally hosed for the better part of a week. There's nothing wrong with my Internet connection; if I manually assign IP addresses, everything works. It's just that clients that require DHCP won't work. So any device without a UI that let's me assign an IP manually is now unusable (which means most of my "smart home" appliances no longer work).

I can tell you this, I'll be a lot more careful about installing firmware updates in the future.