If the spinner on the home page is just spinning, it is a sign that something is wrong with your HealthKit and Health app.
We query HealthKit for data, the spinner indicates that HealthKit never returned the data we needed.
There is a solution by a user to reset the HealthKit, please give it a try:
1. Remove the App from iPhone
2. Restart iPhone
3. Go into Health-App > Datasources>Removed Apps and selected "Delete all Data"
4. Install Sleepmatic app again, and grant all permissions