Problem with hand washing functionality

Hello, I am facing new problem with hand washing app. In the past it worked fine, but a few weeks ago it stopped.

When app detects washing my hands, it correctly starts counting. But when I stop washing (does not matter whether it is shorter or longer than 20 sec), apple logo appears (like when you switch watch on). After a few seconds standard watch dial is displayed again and everything works fine ... till next hand washing:)

Do you have any idea where the problem can be?