A while back I replaced a Deco unit at my house.  When I installed the replacement, I needed to do a firmware update on the new unit.  

After updating the unit and the "restart" none of the devices on my guest network could get IP addresses from the DHCP server.

I restared the deco system again, and the problem went away.

Over the weekend, I added an additional Deco M9 unit to the network, and now my guest network devices can't get DHCP addresses again.  

DHCP is working fine for the main network, but DHCP for the guest is not working.

It takes multiple reboots of the main DECO before the DHCP server works properly on the guest network.