Upgraded to 1.3.0 about 24 hours ago, and for the last 2 hours I've been fighting to get anything at all online.
After some troubleshooting I think I discovered the issue. I use a Linux server as a pi-hole, and what appears to happen is with that much traffic going to the Ethernet LAN, the Deco M5 completely blocks the Ethernet LAN link.
Ethernet Backhaul from the other Decos drop too, and all my hardwired devices can't get Internet or even a DHCP address! Since all the DNS traffic was going to the pi-hole even the wireless devices all quit working.
For now I've set the DNS servers to default, so I'm getting the upstream server IPs when I check settings on my devices. I'll monitor and see if it does this again without the pi-hole, but I have to say this is a SERIOUS bug in this software. To take down the entire wired LAN like that is beyond heavy handed. If that one device was quarantined as a potential problem, sure that I would understand, but this breaks so much stuff to do this.