Expected Behaviour:
Everything's been fine with my PiHole for literally years, but now just today it seems to be disrupting the network to the point that I can't SSH to it or visit the web interface.
Actual Behaviour:
I'm not able to access anything over ethernet (from any machine connected via wired connection) but wifi is weirdly okay. I can't SSH to the Pihole or access the admin interface, either via hostname or IP address. I had to pull power to the network switch that the Pi is connected to (it's connected via PoE) and restart in order to regain (temporary) access. I've done this twice now today. I removed it from my router's DNS and reverted back to 1.1.1.1 so the network is usable.
I haven't made any changes to Pihole in months, I have no idea why it would suddenly freak out. After the first outage I did a pihole -up but it happened again a couple of hours later.
You'll see in the debug log that it reports it can't resolve doubleclick.com but I'm able to ping and curl it fine from the Pihole's terminal.
Unless this is somehow a complete coincidence, something else is disrupting the network, and restarting the network switch that the Pihole is connected to happened to fix the issue elsewhere at the same time.