When using YouTube on iPhone mobile through the Pi-Hole, it is preventing YouTube History to retain what I am watching. Same thing is happening on both iPhones for my sons.
When I'm using YouTube on my Android phone, this is not happening my YouTube History is correctly recording the watched videos. Both iPhones and the Android are logged into their respective YouTube accounts.
Please upload a debug log and post just the token URL that is generated after the log is uploaded by running the following command from the Pi-hole host terminal:
I remember putting some domains in whitelist to allow history and statistics working for youtube. I just checked and saw I have "video-stats.video.google.com" and "video-stats.l.google.com" are whitelisted. May be it helps for your case as well.
I'm experiencing exactly the same problem. My Ubuntu desktop relays/stores history fine, but any IOS device (interestingly, not tvOS) does not seem to work with YouTube's Watch History.