They call it “dark traffic” - ads that are not seen by tech-savvy users who have excellent ad blockers.
Not surprised that its growing. The web is unusable without an ad blocker and its only getting worse, and will continue to get worse every month.
Unless I’m misunderstanding, that doesn’t sound like a bug at all. Outside of a few specific circumstances, devices shouldn’t communicate with anything outside of the given subnet mask. Rejecting traffic outside of that subnet mask is exactly what it should do. And why wouldn’t your pihole be in the same subnet (or at least be included in the subnet mask) for the LAN? You can have the pihole’s IP address be whatever you want, so give it an IP in the same subnet.
I use VLANs and different subnets for security. Having PiHole break randomly every few weeks and seeing the config is different when I didn’t change it was beyond frustrating, so I just gave up