Vivosmart 5: From good to bad stress measurement

I recently bought a Vivosmart 5 and have been finding it underwhelming. As a long-time Garmin user, I'm now considering other brands like Fitbit. The stress tracking feature, in particular, seems to be significantly less accurate than previous models. It frequently reports high stress levels, even during periods of relaxation. This inconsistency is puzzling, especially given my positive experiences with other Garmin devices. Why is the Vivosmart 5's stress algorithm so much less reliable, particularly when compared to my older Vivosmart 4?