Seems to get current update but graph doesn't really update properly. Sometimes not at all, sometimes only few hours of the day
Try this: Change the setting from the interrval (for me from 15 to 1 minute).
Then open the menu on the top left and scroll down to Exit the app.
Then open the app again, wait untill the 1 minute has passed and it shows the HR again, then change back to what you had (15 in my case) and exit again.
Start the app again and it should work now.
Turning it on and off a few times seems to have helped too