Does opening Apple News for the first time re-enable location-based ads? After upgrading to Mojave, I checked around the settings for new features and saw that location-based apple ads (Security &amp; Privacy -> Location Services -> System Services Details) was unticked (I'd unticked it some time ago in a previous version of the OS). Later I opened the new News app to see what it contained, and noticed that the welcome banner said it would use location based ads unless opted out, but I didn't think much of it since I'd already opted out.

Today I checked that setting again and noticed it had become ticked. After unticking it and opening Apple News, it doesn't seem to have been re-ticked again. Is this something it only does the first time News is opened, or have I misidentified the culprit?
Yes.

When you first launch Apple News, there is some small text by the continue button that says: 


  Your location is sent to Apple to provide you with geopgrahically relevant ads in Apple News and Stocks. You can change this in System Preferences.


If you previously had location based Apple ads unticked it will become ticked.