I don't have a Headers phase in my project either, but enabling the new build system did not solve the issue for me.

Thanks for the additional information. It was an outdoor run with a series 6 watch. Are the metrics collected by default and added to the workout or do I need to enabled them (I've tried both)? My min deployment target is 6.1. Does that matter? Thanks, Jeff

Yes, the new running metrics are working great for me. You need a watch series 6 or later (or SE). Make sure you ask for permission for the new types and your using HKLiveWorkoutBuilder. I'm calling enableCollection on the HKLiveWorkoutDataSource, but I don't believe that is necessary.

Well, I can say it's significantly better than when the feature first came out, but it's still too slow, especially if you have something like 100 intervals or more. I actually have a toggle in the app to turn off the feature because of it. What's your use case and what are you seeing?