Elevation data not accurate

When you do the correction in Strava, do the maximum and minimum altitude change much? The reason I'm asking is that any "total ascent/descent" number depends on how you define "ascent" and "descent", and map-based post-exercise calculation almost always create a more "smooth" elevation curve, because of the small resolution of the elevation map (compare to real-time barometric reading). And that can mean less ascent/descent, if the smoothing of the Strava elevation map differs from the smoothing done by the watch to the barometric altitude reading.

I'm not saying your barometric sensor could not be malfunctioning, I'm just saying that there are other possible explanations as well. But it's strange if this only started happening recently. But if the maximum/minimum altitudes are much different after Strave corrections, then there definitely could be something wrong.

Today joined beta and updated to the newest beta software. After installing this activated the elevation widget, remaining indoors on the same floor this seems quit strange also?

I observed similar hike with latest bata SW (17.18), will have to monitor it in coming days. 

Regarding your initial issue - i had exactly he same problem with my previous Forerunner 945 LTE. Calibration, reset of the watch ect. didn't help, eventually Garmin replaced the unit. With the new one, the elevation data was again ok. 

I also have the same problem. If I keep it on my wrist it does this but if I leave it on the desk the altitude remains stable. In my opinion it is a software problem and depends on the fact that the measurement is distorted (incorrectly) by the change in temperature. However, I don't understand why this problem only affects some forerunners and not all. The problem is still when you run outside, in that case the temperature changes a lot and with each drop or increase in temperature the altitude varies for no reason. I contacted garmin and they told me to send it in for service but I'm sure it's not a hardware problem. If a new version doesn't come out after Christmas I will send it for support.

I got my Forerunner replaced under warranty, nee device on same software is working like it should! 

I face a similar problem since version 17.24 and problem still persists with version 17.26. Below is my post as well.

https://forums.garmin.com/sports-fitness/running-multisport/f/forerunner-965/353656/altimeter-problem-in-v-17-24

A friend of mine is also facing this same problem since version 17.24

Since multiple watches are affected I thought it is a software issue but could this be related to a hardware problem?

Did you ever get this resolved? Mine is always out by a few hundred feet doing nothing, worse if running. I calibrate the barometer& altimeter 10 times a day and it's always off an hour later

I got my Forerunner replaced under warranty, new device on same software is working like it should!