Altimeter unstable since 7.60

Mine is not stable as it was previously, but only once a night bounces by a few meters and if I go up and down the stairs (I live at fourth floor) it shows different altitude when I get back up in the appartment, thing that previously was very accurate at.

It is my 3rd one, hope it will not end up like the others, to have to be replaced under warranty. 

Mine is now constantly bouncing, very much different than before. I think it is normal to have a small deviation since the watch decides if an air pressure change is due to walking (=climbing) or due to the air pressure chnges in general. Small misinterpretation of that leads to a minor delta in height. But not 30 meters per 10 seconds as is the case on my watch now :-(

FYI, I tried soaking it in water, and even reset the watch. Still no joy. Also another button got stuck (again) so I'm sending it to service. Second f5+ to go there for me. I hope the third will bring more joy.

My 1st 5X+ has just been replaced for faulty alt/bar/temp sensor. Still waiting for the replacement to be delivered.

What were the symptoms, IE, how bad was it. Mine keeps drifting slowly during activity, so when I finish a ride, at the place where I started, the altitude is about 50 meters less, about 160ft.

For me, the symptom was that whil standing still, the altitide would change with many meters in a very short time (10 seconds). Before that it was actually pretty good. Make sure you understand the functioning of an altimeter and have the appropriate settings. on setting default, it will try to estimate if change in air pressure is due to change in altitude or due to changes in the weather.

Slow drift, up to 5-10-15 meters per hour, can be caused by changes in the ambient air pressure, which is caused by weather and not a fault of the watch. If you enable auto calibration during activity and not just at start of activity, the watch is supposed to try to correct for this.

It can also be caused by drift in the ambient pressure sensor itself. Some earlier Garmin models had a tendency to such drift, when the temperature of the watch changed during the activity, but I haven't been able to provoke that behaviour in my 5X+.

...and lastly, it can be caused by wrong guesses by the watch, when you went up in altitude, the pressure dropped, and the watch guessed that you were still at the same altitude with the change being caused by the weather, or you stayed at the same altitude, the pressure dropped, and the watch guessed that had gone up in altitude with the weather being constant. The watch will have to do this guesswork during the activity because you have one instrument trying to measure two different things. But again, the auto calibration during activity is supposed to improve that.