Why did my Apple Watch stop tracking activity correctly?

Hi, after a little more than one year of use my Apple Watch series 4 (watchOS 7.2) suddenly stopped tracking activity. Basically the Activity app is not detecting any movement (red ring remains at 0), while it detects me standing even while I am sleeping. Also the SleepWatch app is having problems, it detects 100% restful sleep and thinks I am sleeping even when I am just sitting. The red ring appears to be working on. Steps are detected. Heart rate and HRV are detected. The hand washing app seems to be working ok (it starts when I start washing hands and stops if I stop moving the hands). This is to say that I think that the sensors and accelerometers appear to be working, at least to some extent.

I tried to restart the devices after turning off activity tracking, but there was no change.

Is there anything else to check?