Call startUpdatingLocation from CLRegion event

I am trying to work out how to start updating locations when triggered by a CLRegion in iOS 15. The use case is that a user gets to a certain predefined starting point (determined by region monitoring) for a regular journey and then the app startUpdatingLocation, without need for user interaction. In my testing so far, if I call startUpdatingLocation from within didEnterRegion the updates stop within 10.