Weirdly my iPhone is sending out DNS names that are just random gibberish it seems. But obviously I worry about more sinister behaviour. All domains I tried to check fail to resolve.
It might be checking to see if you are in a captive portal (need to log into wifi).
It wasn’t there a few weeks ago and I’m running pi-hole for some months now. So it might be a new app on my phone doing this for some reason like you mentioned? Still a weird tactic right?