Looks like 6.11 breaks Guest networking from working correctly (devices report no internet connection)

Specifically, it is when Local DNS Caching is enabled and in my case I have a custom DNS server on my local network for devices connected to the non-guest wifi SSID. Devices connected to the Guest network get the eero Gateway as a DNS resolver (which they can't reach since subnets on the LAN are isolated).

Eventually, after the DNS lookup timesout against the gateway the query falls back to google public DNS and works, but most devices simply report no internet connection. iOS devices for example continually pop up a warning for no internet connection

Explicitly disabling Local DNS Caching under labs (or turning off HomeKit security) fixes connectivity but this broken behavior started in 6.11