VivoSmart 5 stopped detecting my activity when I go for power walks.

Greetings!

About 4 days ago, my VivoSmart 5 stopped detecting my activity when I go for power walks. The software is up to date — Version 3.31. It captures my overall steps ok, but not that I am doing an activity. I can manually record my walk, but that's not the point.

Any tips? ..vc