The recommended support article doesn't help at all for me: the watch series 4 does measure heart rate, steps, etc. accurately but it simply counts too many flights as of months now. It runs the latest software, it has been restarted, I continuously capture work outs on flat surface. But it is just reporting an excessive amount of flights (100+) day in day out since months. I am quite happy with the watch but I don't like the fact that it is off so much on the flights metric. I live in a flat country (there is hardly any elevation difference) and a climb about 10-20 flights a day which doesn't justify a number over 400. The count is 45 this morning and I only climbed/ascended the stairs in my house 4 times.....
And it did work the first months.
Main difference in my case: I have changed from a woven nylon band to a metal milanese band a few months ago.
Could that be a potential root cause?