Altimeter and elevation issues still occurring (calibration & temperature)

I am having exactly the same issues with my 955. I first noticed that the start / end elevation were always different (even though I start/ end always in the same spot).

My wife has the 255music and the elevation plots look way better (we run together most of the times). I even did a run wearing both watches and the the 955 always drifts.

I believe it's a software problem when using the smart selection (barometer and altimeter). What I noticed is that in reasonably flat runs, the 955 assumes most environmental changes (temperature and pressure) as elevation changes... Maybe the other watches have a different function to determine this?

I'm already in contact with Garmin but after 3 email's I still haven't been able to explain this to the contact centre here in Iberia.

I'll let you know how the situation develops.

Btw, I have a post similar to yours on the forum (beta software for 955)

Here is the link for my post: forums.garmin.com/.../1696771

Same for me. Since firmware 17.xx in Beta I get way to many height changes counted by the watch. This is a screenshot for the last four hours, while the watch sitting on my office desk. 

Sensor cleaning didn’t change anything, but I guess it’s a sw problem. 

For me this is an old Garmin issue. In my case the body temperature increases during the activity what makes the watch gives a lower altitude ate the end of the activity even if it's the same place as start. 

It affects other measures cos the watch will consider I was running "downhill". But in the FR955 the difference is small. It was much bigger in my onld Vivoactive 3. 

The Fenix7 has the sensors better positioned to the side of the case. Maybe that's why they are more accurate.

It mostly seems that is it too sensitive to temperature changes. I went for a short walk yesterday around some neighborhoods (not recording an activity) and the altimeter reading drifted up 35ft by the end of the walk (ending at the same starting location). It was cold outside, so the temperature reading on the watch dropped in the beginning of the walk. This pretty much is the same as most of my recent runs. The temperature graph shows a sharp decline in the beginning of the run and it causes the elevation to drift upward. Winter is starting so it makes sense that this is happening more if the temperature is a major factor. I haven't looked back at my summer runs but I would imagine that the elevation drifts downward if the watch temperature increases during the activity. I guess if the temperature fluctuates both up and down during an activity that it will overestimate both the total ascent and total descent. This is pretty stupid because its an outdoor watch and its so affected by temperature.

Its just annoying because the Fenix series doesnt seem to have the same issue and therefore there is probably some sort of software difference. If anything, I would have expected the Fenix to have worse issues because the sensor is more exposed on the side of the watch.

This is the comparison to the Fenix 6X that I had discussed in my initial post. My F955 Solar is in red (drifting higher) compared to the Fenix 6X in blue.

Im not sure how much I trust Strava elevation corrections, but I added them in for a comparison. The colors changed for the below image. Forerunner (red), Fenix (green), Strava Corrected Elevation (blue). The Fenix looks way closer to Strava:

Here I have screenshots of 3 runs on exactly the same loop. First image is the real profile from a run in July, the other two are with the latest firmware. Temperature was no issue last winter. 

FWIW i have the same issue with my 255M.  Runs usually end up at a higher elevation than the start.

If its a hilly course its not as obvious but somewhere flat its very clear.

My guess is the pressure sensor isnt temperature compensated as as the watch temperature changes during a run it logs this as a change in elevation.

I had exact same issues from may to november. I did this topic about it. Long time i thought it have to be somekind of software bug and it will be fixed soon but no. New software versions came but altimeter problems weren't fixed. In the beginning of november when software 17.xx was released to public beta i did this bug report too. Eventually garmin agreed to repleace my watch under warranty. Now i have new watch since mid november and everything seems to be working fine again. Absolutely no problems at all with elevation or barometric data. So I advise you to contact garmin support. There isn't much help you can get from this forum except maybe confirmation that these altimeter problems exist on some FR955 watches. Dont know why.

I’ve got the 955 forerunner solar and suddenly I’m doing a 40 minute run and it’s recording 56,000m elevation on a 20 metre course !! Consequentlyy TSS is in the thousands !!

we’ve just gone skiing and same again but also I’ve covered circa 40-50km but it says I’ve ski’d 1902km today and again elevation is ridiculous 

any suggestions to correct , greatly welcome , I’ve cleared the sensor hole but no change!! 

I just wonder if it’s a data/ system issue and you have to go and find the first activity it did this and then delete everything since as this was a resolution on 920xt issue a few years back!!