Wrong Floors Calculation in 20.29

I have exactly the same problem.

Same

Several people have reported the same error since the update. I don't think it's a fault with the barometer. However, I will try to test the solutions we discussed.

8634830 said:

Several people have reported the same error since the update

Still might be coincidence.

Personally, I am on 20.29 with my FR 955 and the baro-/altimeter is just fine. During runs it's ok and also counting floors ok. No false floors while in flat area.

(I experience other errors though, see the OHR and the Varia threads)

At least give 9216334s tip a chance. And if it does not work, contact support.garmin.com and claim that the baro-/altimeter is broken.
I would not count on any kind of software fix.

When there are rapid changes in ambient air pressure due to weather and I walk around on the same floor, the watch does count floors, and that has been this way since Fenix 3. 

Distinguishing between true alitude change and barometric (weather) changes is pretty hard. I expect altitude to be 'locked' while the user sleeps, but other than that, I just calibrate the altitude often when it is unstable weather.

You can't exclude that the algorithm was changed in 20.29 and therefore you experience unexpected behavior, but weather changes are more likely, and hardware failure is also unfortunately a possibility, and then you have to contact Support.

Yesterday I went running and the altimeter didn't work properly. I did more than 100 m of elevation difference over the real elevation (checked on a friend's 255)

yesterday i have a run session locked to 16m slm, ita was around 300m d+. looks a related bug in 20.29. now alti/baro seems working.

Just for fun - start activity like running and show on screen altitude (and temperature if you want). Put watch in open fridge and watch as altitude change when temperature drops (like 20meters in just 2 minutes). Its a firmware bug which is with us years and with other forerunners