WatchOS 3 by Tutorials (5-stars) notes…
ISSUE #1: Chp.23 Groundhog. WorkoutSessions continue to run IF user accidentally cancel / dismiss the ActiveWorkout view by touching title – vs – force-touch stop to save/cancel. This is a known watchOS behavior, still an athlete in mid-workout would freak if this happened.
ISSUE #2: Swimming misbehaves. No heartrate. App crashes. Also an Apple watchOS 3 upgrade issue. I believe watchOS 3 workout API has changed significantly for swimming.