22.18 elevation way off

It's certainly possible that my issue is hardware related and not software. But I never had any issues on 21.20, and every run on 21.22 has had the issue. Did the hardware happen to fail the same day I updated to 21.22? It's possible... but that seems like a less likely possibility than this being a firmware issue.

@garmin-sierra — you asked for more reports in this thread, and I did file a ticket with product support, but the only option they have is a paid warranty replacement. I'm happy to help with any sort of debugging here (If there's a way to load 21.20 back onto the watch, I can do that and see if the problem goes away, which would be a smoking gun for a firmware issue), but as of now I'm kinda in limbo.

Can you plot and post a comparison before and after the firmewareupgrade between your GPS reading and your barometric reading as described here:

Altimeter performance test - Forerunner 955 Series - Running/Multisport - Garmin Forums

So you get an indication if the correlation was already weak before and got worse or if it was perfect before the update and really broke. Because as you write, it would be indeed strage if it really startet after the firmware update.

This is my plot. The altitude is so off that the GPS one (real altitude) it is out of graph

Same problem... 

Garmin-Sierra

What's this post and the other mentioned by Stefan.

Could you make a plot of an activity before the software update? Would be interesting to see if there is already an indication of a faulty barometric measurement. Or it really starts with the software.

Your graph looks different to the one of hpaixao. Because his graph in the other thread has some "random" signal superimposed und yours looks similar to the GPS altutide but it generates an offset in the first ten minutels --> thermal acclimatization?.

So a theory: Garmin introduced a temperature compensation with the new firmware, but your internal temeprature readings are wrong, leading to this offset.

Anyways - it seems to be the fact that there are some people owning watches which are more temperature sensitive then others. But i do not know and if those informations could be linked somehow.

In addition, there is data for the device temperature in the fit file. So in one of my examples it looks like this:

So i see a thermal acclimatization within the first 10 minutes. Maybe you can also check, because this would be an indication where your initial drift might come from.

The issue is not related with the update, mine is wrong since day 1 in november 2023

This is temperature. After a transfer in car, I started the run with 2°C outside

Oops, I took you for Dan. Sorry.

So in your case it seems that you have one of the temperature sensitive devices.