I mode trail / hike the "ascent" elevation get stuck. I use the warranty but having the same problem (maybe it's the same watch) Try all different things problem stay.Im' pretty sur the the send me the same watch for warranty :( not appl

You could check the serial number and compare it with the original you had, but to me it does not really look like a hardware problem - the altimeter (the pressure sensor) clearly works on the right watch, because the absolute altitude varies on both watches. I'd tell that the watch failed to detect you ascent, and perhaps considered that you took a lift. There is clearly no problem with the sensor, so it is not surprising the replacement watch did not help.

9772221 said:

I mode trail / hike the "ascent" elevation get stuck

... BTW, using the Hike or Trail for a ski activity is not really a wise choice. These activity profiles expect certain pattern of accelerometer data to help detecting your motion, steps, and cadence. When on ski, the patterns are completely different than what the watch expects. It may then also go into the auto-pause mode, when you move slowly uphill, hence stopping also incrementing the elevation gain (ascent).

Why don't you rather use the corresponding ski activity?

I compare the #serial it's not the same

But the probability to have the same problem on a second watch mean that :

I have no luck

All the watch have the same problem (it common also on Fenix or instinct)

(I detail my answer in your second Post)

First all thanks to your answer 

When I say ski. It's mean skin hiking. So I don't take a lift. I climb with ski and skin outside of a ressort. But the problem is the same regardless off what I have to my feet

Got the same problem the day before with my basket on a basic hike

Altitude on the 2 watch are a little different on the pictures but most of the time they are close enough to be right 

To finish I don't use auto pause

So : got a new watch, same problem, aways here regardless of activity and present on some.other watch

Thx

Not that :

I have a new watch coming for warranty who have the same problem (so reset factory)

And

I have multiple times make an update (automatic with my phone)

And

Do also a reset factory by following the instructions and using a pc 

Problem always happens 

And as I told, you can find the problem on Fenix and instinct which means it's more a software problem than a hardware or configuration problem 

As I wrote, there is no apparent hardware problem with your watch, since the sensor works. So it is expected that the replacement of the watch cannot change anything. However, if you are really using the Hike activity for crosscountry ski, then it is not surprising the recording is wrong. Use the dedicated Cross-Country Ski activity instead. And disable the Auto-Pause.

9772221 said:

Got the same problem the day before with my basket on a basic hike

Again, do not use Hiking for anything else than hiking. If you play basketball, use the Basketball activity profile.