I was using ISC DHCP, and I switched to Kea and all of a sudden many devices on my network cannot reach the Internet.
Once I switched to Kea, certain devices (like my smart tv, 3d printer, one of my 3 iphones) would stop working. I confirmed it has the proper default router, it has the proper DNS server, yet it couldn't access the Internet.
If I switch back to ISC/PiHole for DHCP, it all works fine and all problems go away.
For example, my 3D printer would complain it cannot access the Internet. At the time, I could ping the device, and I can look at the DNS logs and see it querying for DNS. It feels like default router issue, but I confirmed on the device (like the iphone) it is set to the correct default route and dns.