Comment by Abishek_Muthian

Yesterday my home DNS weren't resolving and noticed on PiHole that there were >30,000 requests of *.in-addr.arpa (Reverse DNS Lookup) from the iPhone+iPad of the guest to whom I gave the WiFi access and was saturating the Pi's CPU. I re-enabled rate limiting on PiHole and blocked the request with a filter.

A cursory search on the issue says Bonjour is the culprit, I'm forwarding DNS requests to my PiHole instances on my gateway and latest iOS doesn't seem to like it; I haven't faced such issue earlier and I have this setup for several years now.