Watch Ultra 2, erratic heart rate measurement.

after turning on the sports program, the watch either does not measure at all or starts measuring the heart rate only after a while. There are also cases when heart rate measurement turns off in the middle of sports. I tried everything - I checked all possible options that might prevent measurement, paired/unpaired, checked the privacy settings, rebooted, checked the watch by connecting it to another phone, also disconnected it from the phone and tried it on another person, but the situation did not change - heart rate measurement takes place then when the clock wants. All latest updates also installed.

went to local Apple store, but technicians didn't find anything.