Inaccurate floors climbed from day 1

Whilst I use a 965 , I also find it "hit and miss" so to say.  Effectively it relies on Barometric pressure changes which is not always accurate it seems.

Many time I change floors in the house with no reading.

One accepts a % variance from reality and just looks at trends over time in activity levels.

I am not sure what you mean by very inaccurate , I haven't counted during a day before going outside to see , and for example when running outside the movement in elevation is considered a floor movement so its not possible after that stage.

I do notice in the morning sometimes I may have been up and down two or three times but only one floor count shows.

I do believe there is a floor climbing activity but I havent used that specifically.

In my experience, the 255 is quite similar to other Garmin watches when it comes to floor counting. What it does, is to measure changes in pressure while you move you arm. You could get floors in an elevator if you just jog your watch arm. You can also walk up several stairs with no count if you slide your arm on a hand rail. If you walk outside in windy conditions, you can get lots of floors on flat ground. These shortcomings are expected based on the measurement concept used.

I think it's a bit coarse-grained in that you need to be going for a reasonable duration and rate of change to count as a floor, based on some assumptions about a normal flight of stairs. When walking around in regular watch mode, I don't think it counts gradual climbs nor adds together multiple short stairs (e.g. in a terraced landscape). But, climbing a steeper incline will register.

And there is a delay for these stats to update in watch mode. I can get up, walk through my house, climb the stairs, and walk  through the upstairs before the steps or floor metric will change on a CIQ watchface. They'll increment once on my way back down and then the steps will jump once more after I've sat for a bit.

There isn't an issue about delays , it's the fact that the watch isn't accurate as it isn't  counting any floors ....I  walk up and downstairs  roughly 10-15x a day yet the device says I've walked 2 floors up and 0 floors down ?! I don't hold the handrail going up or downstairs ......It's v inaccurate !  Our floors are greater than 3m so in practice it should count the floors but it doesn't .  Hoping other Garmin watches are more accurate in counting floors! I used to own Fitbits which were more accurate !

Yes, if your stairs are only 90 percent of regular Garmin stairs, you can walk up and down 100 times, and the count will still be zero.

Garmin floor is 3m...my floors are greater than 3m...it should measure it but it doesn't measure most of the time .

I would say in general - all my Garmin watches (vivoactive3-4, 255) count floors poorly/inaccurately. And usually down is considered more than up. They also mock me - maybe it would be better for you to walk up and not take the elevator?
My home mountain - where I go quite often - is 660 m of pure ascent, fr255 defines 70-90 floors up, 120-140 down. One china watch for a third of the price shows 220 up and 220 down. Plus or minus 5 floors. Funny, isn't it?

There are some tips that may help you improving the accuracy of floors climbing, in the thread What's the secret to tracking stairs accurately?

Excellent ! Many thanks for the helpful tips and explanation !