Sometimes the app doesn't remain on screen or not recording well. It can be because wearing on top of a wetsuit or Health authorization is not activated (for privacy reasons).
In this case, it is needed to switch off a setting called Wrist Detection.
Also, be sure to follow these instructions:
https://waterspeed.crunch.help/en/issue-with-hr-and-calories/heart-rate-or-calories-are-not-working
