Pixel Watch heart rate measurement not working

I'm recently experiencing the same issue as described in this thread: https://googlesupport.serverhump.com/googlepixelwatch/thread/232722169?hl=en

The green light on the back of the watch suddenly stopped flashing and therefore heart rate measurement isn't working anymore (just showing two dashes).

I also contacted the support and was also bounced between the Pixel Watch and Fitbit team.

This is the last case I've opened: 6-9383000037755

As I cannot find a proper history of my opened cases, I can't provide a case number of any other cases.

As I also suspect a hardware defect of the watch which was part of a promotion, what's the proper way to get this resolved?

Kind Regards

Matthias