Issues with IoT things since Pi-hole update

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Standard pihole installation - running

Pi-hole [v5.5]
FTL [v5.10.2]
Web Interface [v5.7]

On a Ubuntu 20.04 VM, ESXi 6.5, Dell r720
Unifi UDMPro, 24 port Unifi switch, 4 Unifi flex-HD APs
separate vlans for main network and IoT network, and separate address spaces., etc.

Expected Behaviour:

14 OCT - UPDATE - On my network, I changed the DNS server from my local pi-hole to, and both the thermostat and the Tailwind came online immediately and can be accessed through their apps. What should I check in pi-hole to track this down?

Prior to upgrading to the above versions, all my IoT things were working fine. Specifically Nest thermostat and Tailwind garage opener/smart device. I could access them through their respective apps whether on the same network or outside the network.

Actual Behaviour:

After upgrading, the Nest thermostat and the Tailwind device both still connect to the Unifi network, but cannot go outside the vlan to the internet. In Unifi I can see both devices, and they have the same IP addresses on the right vlans as they always have. Disabling iphole for several minutes, then resetting the thermostat with it disabled will allow it to reach the google mothership, register, get a key for the app, and I can get to it in the app. After enabling pihole, within a few hours that connection goes away. The app shows it to be offline, but the Nest itself is still on my local network - connected, same IP, etc.

I've looked at the logs while forcing the Nest to go connect to it's home servers. I see several nest/google entries, but nothing is being blocked - there are no blocked queries with nest anywhere in them. Soooo, it's able to reach out but incoming traffic isn't accepted? I've done as much searching as I can handle and all I'm finding are issues getting the Nest on wifi at all.

I'm new at all this, I believe that the debug log uploads itself without me taking action. Thanks in advance for the help.

Debug Token:

I would start by rebooting the modem and the router. This does not sound like a DNS issue to me.

Me either - I rebooted everything a few days ago, and rebooted them all again this morning.