Apple Watch Series 4 counts stairs badly - WHY?!?

I've noticed that since switching from my Fitbit to the Apple Watch series 4, my stair climbing record has been VERY different.

It turns out that lots of people are having problems with accurate stair climbing reporting on their Apple Watches. As an aggregate of my hunting for info, the best info I could find was that the Watch recognizes stair "flights" as 3 meters - or approximately 16 steps (which is wrong in my house) - and can distinguish stair climbing from hill climbing (apparently Fitbit does not make this distinction).

So after this morning - when I definitely had climbed our stairs more than twice (15 steps per floor) - my Activity app read 2 flights... but who knows, maybe I misremembered how many times I'd been up and down.

So I decided to test it. I climbed our 15-step flight five times in quick succession, pausing about a second before coming down and then again before starting back up. Five flights, 15 stairs, no ambiguity.

After this, my Activity app read 3 Flights, rather than the 8 flights I'd have expected. It only counted one of the five flights I climbed.

My phone and watch sync fine, everything else works as expected, I don't want to recalibrate but I don't believe that's the issue.

Interestingly, my Health app on the iPhone reflects FIVE floors climbed, though it only shows three of those floors being reported by the Apple Watch. Presumably I did climb more flights with the phone in my pocket and those were registered in Health - but they aren't reflected in Activity.

So I just repeated the test with my phone in my pocket. Climbed those same stairs up and back five times. This time neither the watch NOR the phone captureD even a single flight.

So what gives? Does anyone have any insight into this?

• Do my 15-stair flights not count at all?
• If it can't count FLIGHTS of fewer than 16 steps, why aren't the stair steps I take counted cumulatively?
• Is going back down the steps immediately somehow "unwinding" the step count? (insane idea)
• Is there actually some conflict in the data between the watch and the phone that is canceling things out?

Is there a way to deal with this at all, or does the Apple stair climbing function just stink to high heaven and I simply have to deal with it?