Elevation consistently inaccurate (reading too low)

Yes, get the same problem.  I notice this more on a mountain bike ride with lots of elevation change as the Instinct smoothes it out.  Hiking or road riding seems to be much better. Mentioned it a few times on these forums (old version) and seems like others don't notice this as much. For every mountain bike ride I record on Garmin connect I use the elevation correction feature which always results in big difference. 

Guess it puts others off purchasing an instinct when the figures are so different on a group ride.

The weirdest thing is that the inaccuracies seem to be somewhat consistent. For example, when I take one route to the summit, the elevation is lower, but when I take a different route it's almost what it should be. It's like the watch is ignoring elevation gain in specific locations, but it's also accounting for that ignored gain during a descent, hence why the starting and finishing elevation is pretty much the same, as it should be. 

This is honestly a pretty big deal for me. Altimeter was one of the reasons why I bought this watch. 

I recently noticed a somewhat similar problem. Usually the altimeter works as expected (verified it with maps and description of trails the few times I hiked in places that are not as pancake flat as where I live) but every once in a while, when I do steps on a set of steps nearby (outside) it seems to ignore part of the repeats on the steps, and this is where I recognize similarities with the problem you are describing.

What I do is walk 15 minutes to this outside steps, and then do repeats over these steps for one hour, before walking other 15 minutes back home. The elevation gain for each repeat is something like 5-6 meters, and most of the times I see the right elevation and I can see in the altimeter graph on connect the usual pattern of going up and down some stairs for one hour. Other times, the minority of times but still noticeable, I get less total elevation gain, and if I look at the graph there are much less up and downs than it should be.

Edit: I am on firmware 4.00, Sensor HUB 1.11

Yes, I have noticed 2 issues with elevation tracking during an activity:

1)  There appears to be a revised smoothing algorithm (maybe since v 3.1 ) that stalls elevation gain when there is a transition from down to up.  On earlier versions (2.6 and 2.8) the elevation gain on my trail runs and bike rides was excellent - matching the expected elevation gain on those routes, At that time, my Instinct was much better than my Edge which often over-counted gain.

2) As we get into warmer weather, I'm noticing weird jumps/drops in the elevation profile, particularly after 30 minutes of activity.  I suspect this is related to sweat interfering with the sensor.  I'm going to try running with a wrist band to absorb sweat to see if this helps.

If someone has good examples of the smoothing issues, it would be wise to open a ticket with Garmin Support.  

Well,I thought that sweat was the cause in my case as well, but that would cause the starting and finishing elevation to be drastically different. 

Yup, it's disabled. Besides, it would only correct elevation once the activity is uploaded, right? It wouldn't affect what I'm seeing on the watch as I ride. 

Elevation correction is disabled by default on the Instinct so uploading an activity always uses the elevation recorded on the device.  I then correct the elevation using this feature which then shows a more accurate track.  I have never had the need to do this using the Fenix.  

This is my last ride (had an involuntary dismount so will be no exercise for a week or so):

https://connect.garmin.com/modern/activity/3649137269

455m recorded elevation change.  575m corrected.

Uploaded Elevation:

Corrected Elevation:

Garmin Instinct:
Hello, I have a problem with the altimeter of the instinct.
To me, he's unreliable.
I have been hiking since the beginning ( December 2018) with an Etrex Touch 35T, which is reliable and gives me full satisfaction when compared to a map.
I think there is a problem in the design of the Alti / Baro sensor part.
I am at the second Instinct, the first one was exchanged with me by the after-sales service, following the same altimetry problem.
I systematically calibrate my equipment at the beginning of the hike, according to the known altitude, or the map.
On most of the hikes I encountered problems of stalling, as if I had suddenly descended to 10, 50, 100 m underground,... or if I had flown 200 m into the sky....
The hikes where this happened are often hikes where it rains, where I sweated a lot (coat etc...), where it was cold (significant temperature difference = condensation??).
I also realized that the altimeter starts to "malfunction" (and that's normal, of course) when I swim in the pool (I know that's normal there), I find that when I take a shower by running water over the Garmin, I also find myself with this "problem".
Until the sensor is dry....
For me, as a non-engineer, I think the functioning of the sensor is affected by this.
I had a lot less altimeter problem with my old Casio SGW-400H-1BVER
www.casio-europe.com/.../
The rare times I don't encounter any problems, are the times when I don't have time to really sweat (1, 2 or 3 km), or in good weather.....
Another problem is that as soon as the atmospheric pressure increases or decreases during the ride, by 1 or 2 millibars for example, the watch does not readjust (unlike my Etrex).
I find myself at the finish with several dozen meters of differences (logical)....
For example, on May 12 I did a hike (a loop) of 2h28mn and 15 Km, the pressure increased by 2 millibars, it went from 1033 mbar to 1035 mbar, and the Instinct did not readjust (unlike my Etrex), which resulted in a difference of 20 m in height upon arrival (return to the starting point)...
Is it possible to deactivate the altimeter sensor?
Is it possible to use GPS altitude?
Are there any software fixes planned?
A watch for the adventurers? Seriously.....
Sincerely.

Translated with www.DeepL.com/Translator

Bonjour, je rencontre un problème avec l’altimètre de l’instinct.
Pour moi, il n’est pas fiable.
Je randonne depuis le début ( décembre 2018) avec en parallèle un Etrex Touch 35T, qui est fiable et me donne toute satisfaction quand je le compare à une carte.
Je pense qu’il y a un problème dans la conception de la partie capteur Alti / Baro.
J’en suis à la deuxième Instinct, la première m’a été échangé par le SAV, suite au même problème d’altimétrie.
Je calibre systématiquement mes appareils en début de randonnée, en fonction de l’altitude connue, ou de la carte.
Sur la plupart des randonnées j’ai rencontré des problèmes de décroché, comme ci j’étais descendu subitement à 10, 50, 100 m sous terre,…. ou si je m’étais envolé à 200 m dans le ciel….
Les randonnées où cela c’est produit sont souvent des randonnées où il pleut, où j’ai beaucoup transpiré (manteau etc…), où il faisait froid (différence de température importante = condensation??).
Je me suis également rendu compte, que l’altimètre se met à “dysfonctionner” (et ça bien sur, c’est normal) quand je nage à la piscine (je sais que là c’est normal), je constate que quand je prend une douche en faisant ruisseler l’eau sur la Garmin, je me retrouve également avec ce “problème”.
Jusqu’à se que le capteur soit bien sec…
Pour moi qui ne suis pas ingénieur, je pense que le fonctionnement du capteur est impacté par ça.
J’avais beaucoup moins de problème d’altimètre avec ma vieille Casio SGW-400H-1BVER
www.casio-europe.com/.../
Les rares fois ou je ne rencontre pas de problèmes, sont les fois où je n’ai pas le temps de vraiment transpirer (1, 2 ou 3 km), où par beau temps….
Un autre problème étant que dès que la pression atmosphérique augmente ou baisse lors de la randonnée, de 1 ou deux millibars par exemple, la montre ne réajuste pas (contrairement à mon Etrex).
Je me retrouve à l’arrivé avec plusieurs dizaine de mètres de différences (logique)…
Par exemple le 12 mai j’ai effectué une randonnée (une boucle) de 2h28mn et 15 Km, la pression à augmenté de 2 millibars, elle est passée de 1033 mbar à 1035 mbar , et l’Instinct n’a pas réajusté (contrairement à mon Etrex), ce qui a eu pour conséquence une différence de 20 m de hauteur à l’arrivé (retour au point de départ)…
Y a t’il possibilité de désactiver, le capteur altimètre?
Y a t’il possiblitité d’utiliser l’altitude GPS?
Y a t’il des correction de logiciel de prévu?
Une montre pour les baroudeurs? sérieusement...
Cordialement.

The default isn't always un"corrected", at least not historically. The Connect website have gotten it wrong before and turned it on even if you have a barometer watch, that's why I asked.

So it seems the Instinct might be smoothing the elevation curve.. something to bring up with the beta team?