Ultra Watch 2 Black - Running heart rate measurement inaccurate

After owning several regular Apple Watches and being very happy with each of them, this autumn I thought I would upgrade to the latest Ultra 2 in black with the titanium watchband.

Very much both to my surprise and disappointment, the watch does not measure my heart rate accurately, especially during outdoor running workouts. Partially, this seems to be due to the titanium watchband which affects the performance of the sensor (as I found out here: https://youtu.be/KQrYl-AdhQw?si=Z1FhBKLo0e99QFet). Also the watch in general seems to have issues with accuracy when it comes to measuring heart rates.

But there seem to be more issues, even when using it with other watchbands from old Apple Watches (which did the job perfectly fine and seem to be more accurate according to the review just posted), as well as the latest Ocean watch band.

The inaccuracy of the measurements also seems to get worse when running outdoor in the cold, with the watch covered up by long sleeves or gloves. This is for me really a problem since I can not trust the measurements of the watch any longer -- which sometimes might be accurate, but are often clearly inaccurate and totally off -- as well as other inferences that come along as especially VO2 max values.

Sleep tracking seems to be OK, as well as other heart rate related measurements which involve less movement (I guess?).

Finally, the issue seems have to become much worse with the last software update (watch OS 11.2). I am wondering if other users experience the same.

While I generally think the watch has many great features such as an excellent screen, great aesthetics, and a much better battery life than the regular watch (which is super important if you were it all the time like me), it is extremely disappointing that the black Ultra Watch 2 is not capable of measuring outdoor running workouts as accurate as its much cheaper predecessors or the current Watch 10.