Stride does not store any of your data, it simply displays your workouts directly from HealthKit. We do use a third party crash reporting tool to help us diagnose issues and improve user experience.
Stride will share your data when you choose to upload a workout to Strava. At this point we convert the selected workout into a compatible format and upload it to them. This is the only time we will share any of your data with a third party.
If you have any questions or suggestions you can contact us at instepapp@gmail.com.